diff --git a/SabreTools.DatFiles/DatFile.cs b/SabreTools.DatFiles/DatFile.cs
index 9c628d8e..f4e6f2ad 100644
--- a/SabreTools.DatFiles/DatFile.cs
+++ b/SabreTools.DatFiles/DatFile.cs
@@ -250,7 +250,7 @@ namespace SabreTools.DatFiles
                 if (rom.GetFieldValue<long?>(Models.Metadata.Rom.SizeKey) == null && !rom.HasHashes())
                 {
                     // No-op, just catch it so it doesn't go further
-                    logger.Verbose($"{Header.FileName}: Entry with only SHA-1 found - '{rom.GetName()}'");
+                    logger.Verbose($"{Header.GetFieldValue<string?>(DatHeader.FileNameKey)}: Entry with only SHA-1 found - '{rom.GetName()}'");
                 }
 
                 // If we have a rom and it's missing size AND the hashes match a 0-byte file, fill in the rest of the info
@@ -271,7 +271,7 @@ namespace SabreTools.DatFiles
                 // If the file has no size and it's not the above case, skip and log
                 else if (rom.GetFieldValue<ItemStatus>(Models.Metadata.Rom.StatusKey) != ItemStatus.Nodump && (rom.GetFieldValue<long?>(Models.Metadata.Rom.SizeKey) == 0 || rom.GetFieldValue<long?>(Models.Metadata.Rom.SizeKey) == null))
                 {
-                    logger.Verbose($"{Header.FileName}: Incomplete entry for '{rom.GetName()}' will be output as nodump");
+                    logger.Verbose($"{Header.GetFieldValue<string?>(DatHeader.FileNameKey)}: Incomplete entry for '{rom.GetName()}' will be output as nodump");
                     rom.SetFieldValue<ItemStatus>(Models.Metadata.Rom.StatusKey, ItemStatus.Nodump);
                 }
 
@@ -280,7 +280,7 @@ namespace SabreTools.DatFiles
                     && rom.GetFieldValue<long?>(Models.Metadata.Rom.SizeKey) != null && rom.GetFieldValue<long?>(Models.Metadata.Rom.SizeKey) > 0
                     && !rom.HasHashes())
                 {
-                    logger.Verbose($"{Header.FileName}: Incomplete entry for '{rom.GetName()}' will be output as nodump");
+                    logger.Verbose($"{Header.GetFieldValue<string?>(DatHeader.FileNameKey)}: Incomplete entry for '{rom.GetName()}' will be output as nodump");
                     rom.SetFieldValue<ItemStatus>(Models.Metadata.Rom.StatusKey, ItemStatus.Nodump);
                 }
 
diff --git a/SabreTools.DatFiles/DatHeader.cs b/SabreTools.DatFiles/DatHeader.cs
index 5577fcd8..4adb42a5 100644
--- a/SabreTools.DatFiles/DatHeader.cs
+++ b/SabreTools.DatFiles/DatHeader.cs
@@ -23,6 +23,11 @@ namespace SabreTools.DatFiles
         /// </summary>
         public const string AddExtensionKey = "ADDEXTENSION";
 
+        /// <summary>
+        /// External name of the DAT
+        /// </summary>
+        public const string FileNameKey = "FILENAME";
+
         /// <summary>
         /// Output the machine name
         /// </summary>
@@ -62,13 +67,6 @@ namespace SabreTools.DatFiles
 
         #region Fields
 
-        /// <summary>
-        /// External name of the DAT
-        /// </summary>
-        [JsonProperty("filename", DefaultValueHandling = DefaultValueHandling.Include)]
-        [XmlElement("filename")]
-        public string? FileName { get; set; }
-
         /// <summary>
         /// Read or write format
         /// </summary>
@@ -168,7 +166,6 @@ namespace SabreTools.DatFiles
         {
             var header = new DatHeader()
             {
-                FileName = this.FileName,
                 DatFormat = this.DatFormat,
 
                 InputDepot = this.InputDepot?.Clone() as DepotInformation,
@@ -185,6 +182,7 @@ namespace SabreTools.DatFiles
             header.SetFieldValue<bool?>(Models.Metadata.Header.DebugKey, GetFieldValue<bool?>(Models.Metadata.Header.DebugKey));
             header.SetFieldValue<string?>(Models.Metadata.Header.DescriptionKey, GetFieldValue<string?>(Models.Metadata.Header.DescriptionKey));
             header.SetFieldValue<string?>(Models.Metadata.Header.EmailKey, GetFieldValue<string?>(Models.Metadata.Header.EmailKey));
+            header.SetFieldValue<string?>(DatHeader.FileNameKey, GetFieldValue<string?>(DatHeader.FileNameKey));
             header.SetFieldValue<MergingFlag>(Models.Metadata.Header.ForceMergingKey, GetFieldValue<MergingFlag>(Models.Metadata.Header.ForceMergingKey));
             header.SetFieldValue<NodumpFlag>(Models.Metadata.Header.ForceNodumpKey, GetFieldValue<NodumpFlag>(Models.Metadata.Header.ForceNodumpKey));
             header.SetFieldValue<PackingFlag>(Models.Metadata.Header.ForcePackingKey, GetFieldValue<PackingFlag>(Models.Metadata.Header.ForcePackingKey));
@@ -227,7 +225,6 @@ namespace SabreTools.DatFiles
         {
             var header = new DatHeader()
             {
-                FileName = this.FileName,
                 DatFormat = this.DatFormat,
             };
             header.SetFieldValue<string?>(Models.Metadata.Header.AuthorKey, GetFieldValue<string?>(Models.Metadata.Header.AuthorKey));
@@ -236,6 +233,7 @@ namespace SabreTools.DatFiles
             header.SetFieldValue<string?>(Models.Metadata.Header.DateKey, GetFieldValue<string?>(Models.Metadata.Header.DateKey));
             header.SetFieldValue<string?>(Models.Metadata.Header.DescriptionKey, GetFieldValue<string?>(Models.Metadata.Header.DescriptionKey));
             header.SetFieldValue<string?>(Models.Metadata.Header.EmailKey, GetFieldValue<string?>(Models.Metadata.Header.EmailKey));
+            header.SetFieldValue<string?>(DatHeader.FileNameKey, GetFieldValue<string?>(DatHeader.FileNameKey));
             header.SetFieldValue<MergingFlag>(Models.Metadata.Header.ForceMergingKey, GetFieldValue<MergingFlag>(Models.Metadata.Header.ForceMergingKey));
             header.SetFieldValue<NodumpFlag>(Models.Metadata.Header.ForceNodumpKey, GetFieldValue<NodumpFlag>(Models.Metadata.Header.ForceNodumpKey));
             header.SetFieldValue<PackingFlag>(Models.Metadata.Header.ForcePackingKey, GetFieldValue<PackingFlag>(Models.Metadata.Header.ForcePackingKey));
@@ -283,8 +281,8 @@ namespace SabreTools.DatFiles
             if (datHeader == null)
                 return;
 
-            if (!string.IsNullOrEmpty(datHeader.FileName))
-                FileName = datHeader.FileName;
+            if (!string.IsNullOrEmpty(datHeader.GetFieldValue<string?>(DatHeader.FileNameKey)))
+                SetFieldValue<string?>(DatHeader.FileNameKey, datHeader.GetFieldValue<string?>(DatHeader.FileNameKey));
 
             if (!string.IsNullOrEmpty(datHeader.GetFieldValue<string?>(Models.Metadata.Header.NameKey)))
                 SetFieldValue<string?>(Models.Metadata.Header.NameKey, datHeader.GetFieldValue<string?>(Models.Metadata.Header.NameKey));
@@ -859,7 +857,9 @@ namespace SabreTools.DatFiles
         /// <returns>String containing the new filename</returns>
         private string CreateOutFileNamesHelper(string outDir, string extension, bool overwrite)
         {
-            string? filename = string.IsNullOrEmpty(FileName) ? GetFieldValue<string?>(Models.Metadata.Header.DescriptionKey) : FileName;
+            string? filename = string.IsNullOrEmpty(GetFieldValue<string?>(DatHeader.FileNameKey))
+                ? GetFieldValue<string?>(Models.Metadata.Header.DescriptionKey)
+                : GetFieldValue<string?>(DatHeader.FileNameKey);
 
             // Strip off the extension if it's a holdover from the DAT
             if (Utilities.HasValidDatExtension(filename))
diff --git a/SabreTools.DatFiles/Formats/AttractMode.Writer.cs b/SabreTools.DatFiles/Formats/AttractMode.Writer.cs
index 6a00cb26..2b47c2d9 100644
--- a/SabreTools.DatFiles/Formats/AttractMode.Writer.cs
+++ b/SabreTools.DatFiles/Formats/AttractMode.Writer.cs
@@ -126,7 +126,7 @@ namespace SabreTools.DatFiles.Formats
             {
                 Name = rom.GetFieldValue<Machine>(DatItem.MachineKey)!.GetFieldValue<string?>(Models.Metadata.Machine.NameKey),
                 Title = rom.GetFieldValue<Machine>(DatItem.MachineKey)!.GetFieldValue<string?>(Models.Metadata.Machine.DescriptionKey),
-                Emulator = Header.FileName,
+                Emulator = Header.GetFieldValue<string?>(DatHeader.FileNameKey),
                 CloneOf = rom.GetFieldValue<Machine>(DatItem.MachineKey)!.GetFieldValue<string?>(Models.Metadata.Machine.CloneOfKey),
                 Year = rom.GetFieldValue<Machine>(DatItem.MachineKey)!.GetFieldValue<string?>(Models.Metadata.Machine.YearKey),
                 Manufacturer = rom.GetFieldValue<Machine>(DatItem.MachineKey)!.GetFieldValue<string?>(Models.Metadata.Machine.ManufacturerKey),
diff --git a/SabreTools.DatFiles/Formats/SeparatedValue.Writer.cs b/SabreTools.DatFiles/Formats/SeparatedValue.Writer.cs
index cb14de42..3a1313d3 100644
--- a/SabreTools.DatFiles/Formats/SeparatedValue.Writer.cs
+++ b/SabreTools.DatFiles/Formats/SeparatedValue.Writer.cs
@@ -159,7 +159,7 @@ namespace SabreTools.DatFiles.Formats
         {
             var row = new Models.SeparatedValue.Row
             {
-                FileName = Header.FileName,
+                FileName = Header.GetFieldValue<string?>(DatHeader.FileNameKey),
                 InternalName = Header.GetFieldValue<string?>(Models.Metadata.Header.NameKey),
                 Description = Header.GetFieldValue<string?>(Models.Metadata.Header.DescriptionKey),
                 GameName = disk.GetFieldValue<Machine>(DatItem.MachineKey)!.GetFieldValue<string?>(Models.Metadata.Machine.NameKey),
@@ -187,7 +187,7 @@ namespace SabreTools.DatFiles.Formats
         {
             var row = new Models.SeparatedValue.Row
             {
-                FileName = Header.FileName,
+                FileName = Header.GetFieldValue<string?>(DatHeader.FileNameKey),
                 InternalName = Header.GetFieldValue<string?>(Models.Metadata.Header.NameKey),
                 Description = Header.GetFieldValue<string?>(Models.Metadata.Header.DescriptionKey),
                 GameName = media.GetFieldValue<Machine>(DatItem.MachineKey)!.GetFieldValue<string?>(Models.Metadata.Machine.NameKey),
@@ -215,7 +215,7 @@ namespace SabreTools.DatFiles.Formats
         {
             var row = new Models.SeparatedValue.Row
             {
-                FileName = Header.FileName,
+                FileName = Header.GetFieldValue<string?>(DatHeader.FileNameKey),
                 InternalName = Header.GetFieldValue<string?>(Models.Metadata.Header.NameKey),
                 Description = Header.GetFieldValue<string?>(Models.Metadata.Header.DescriptionKey),
                 GameName = rom.GetFieldValue<Machine>(DatItem.MachineKey)!.GetFieldValue<string?>(Models.Metadata.Machine.NameKey),
diff --git a/SabreTools.DatTools/DatFileTool.cs b/SabreTools.DatTools/DatFileTool.cs
index e86e4708..c7a2570b 100644
--- a/SabreTools.DatTools/DatFileTool.cs
+++ b/SabreTools.DatTools/DatFileTool.cs
@@ -105,7 +105,7 @@ namespace SabreTools.DatTools
             Dictionary<string, List<string>> itemFieldNames,
             bool onlySame)
         {
-            InternalStopwatch watch = new($"Replacing items in '{intDat.Header.FileName}' from the base DAT");
+            InternalStopwatch watch = new($"Replacing items in '{intDat.Header.GetFieldValue<string?>(DatHeader.FileNameKey)}' from the base DAT");
 
             // If we are matching based on DatItem fields of any sort
             if (itemFieldNames.Any())
@@ -221,7 +221,7 @@ namespace SabreTools.DatTools
             else
                 datFile.Items.BucketBy(ItemKey.CRC, DedupeType.None);
 
-            InternalStopwatch watch = new($"Comparing '{intDat.Header.FileName}' to base DAT");
+            InternalStopwatch watch = new($"Comparing '{intDat.Header.GetFieldValue<string?>(DatHeader.FileNameKey)}' to base DAT");
 
             // For comparison's sake, we want to a the base bucketing
             if (useGames)
@@ -378,8 +378,8 @@ namespace SabreTools.DatTools
             InternalStopwatch watch = new("Initializing duplicate DAT");
 
             // Fill in any information not in the base DAT
-            if (string.IsNullOrEmpty(datFile.Header.FileName))
-                datFile.Header.FileName = "All DATs";
+            if (string.IsNullOrEmpty(datFile.Header.GetFieldValue<string?>(DatHeader.FileNameKey)))
+                datFile.Header.SetFieldValue<string?>(DatHeader.FileNameKey, "All DATs");
 
             if (string.IsNullOrEmpty(datFile.Header.GetFieldValue<string?>(Models.Metadata.Header.NameKey)))
                 datFile.Header.SetFieldValue<string?>(Models.Metadata.Header.NameKey, "datFile.All DATs");
@@ -389,7 +389,7 @@ namespace SabreTools.DatTools
 
             string post = " (Duplicates)";
             DatFile dupeData = DatFile.Create(datFile.Header);
-            dupeData.Header.FileName += post;
+            dupeData.Header.SetFieldValue<string?>(DatHeader.FileNameKey, dupeData.Header.GetFieldValue<string?>(DatHeader.FileNameKey) + post);
             dupeData.Header.SetFieldValue<string?>(Models.Metadata.Header.NameKey, dupeData.Header.GetFieldValue<string?>(Models.Metadata.Header.NameKey) + post);
             dupeData.Header.SetFieldValue<string?>(Models.Metadata.Header.DescriptionKey, dupeData.Header.GetFieldValue<string?>(Models.Metadata.Header.DescriptionKey) + post);
             dupeData.Items = [];
@@ -467,8 +467,8 @@ namespace SabreTools.DatTools
             InternalStopwatch watch = new("Initializing all individual DATs");
 
             // Fill in any information not in the base DAT
-            if (string.IsNullOrEmpty(datFile.Header.FileName))
-                datFile.Header.FileName = "All DATs";
+            if (string.IsNullOrEmpty(datFile.Header.GetFieldValue<string?>(DatHeader.FileNameKey)))
+                datFile.Header.SetFieldValue<string?>(DatHeader.FileNameKey, "All DATs");
 
             if (string.IsNullOrEmpty(datFile.Header.GetFieldValue<string?>(Models.Metadata.Header.NameKey)))
                 datFile.Header.SetFieldValue<string?>(Models.Metadata.Header.NameKey, "All DATs");
@@ -489,7 +489,7 @@ namespace SabreTools.DatTools
             {
                 string innerpost = $" ({j} - {inputs[j].GetNormalizedFileName(true)} Only)";
                 DatFile diffData = DatFile.Create(datFile.Header);
-                diffData.Header.FileName += innerpost;
+                diffData.Header.SetFieldValue<string?>(DatHeader.FileNameKey, diffData.Header.GetFieldValue<string?>(DatHeader.FileNameKey) + innerpost);
                 diffData.Header.SetFieldValue<string?>(Models.Metadata.Header.NameKey, diffData.Header.GetFieldValue<string?>(Models.Metadata.Header.NameKey) + innerpost);
                 diffData.Header.SetFieldValue<string?>(Models.Metadata.Header.DescriptionKey, diffData.Header.GetFieldValue<string?>(Models.Metadata.Header.DescriptionKey) + innerpost);
                 diffData.Items = [];
@@ -571,8 +571,8 @@ namespace SabreTools.DatTools
             InternalStopwatch watch = new("Initializing no duplicate DAT");
 
             // Fill in any information not in the base DAT
-            if (string.IsNullOrEmpty(datFile.Header.FileName))
-                datFile.Header.FileName = "All DATs";
+            if (string.IsNullOrEmpty(datFile.Header.GetFieldValue<string?>(DatHeader.FileNameKey)))
+                datFile.Header.SetFieldValue<string?>(DatHeader.FileNameKey, "All DATs");
 
             if (string.IsNullOrEmpty(datFile.Header.GetFieldValue<string?>(Models.Metadata.Header.NameKey)))
                 datFile.Header.SetFieldValue<string?>(Models.Metadata.Header.NameKey, "All DATs");
@@ -582,7 +582,7 @@ namespace SabreTools.DatTools
 
             string post = " (No Duplicates)";
             DatFile outerDiffData = DatFile.Create(datFile.Header);
-            outerDiffData.Header.FileName += post;
+            outerDiffData.Header.SetFieldValue<string?>(DatHeader.FileNameKey, outerDiffData.Header.GetFieldValue<string?>(DatHeader.FileNameKey) + post);
             outerDiffData.Header.SetFieldValue<string?>(Models.Metadata.Header.NameKey, outerDiffData.Header.GetFieldValue<string?>(Models.Metadata.Header.NameKey) + post);
             outerDiffData.Header.SetFieldValue<string?>(Models.Metadata.Header.DescriptionKey, outerDiffData.Header.GetFieldValue<string?>(Models.Metadata.Header.DescriptionKey) + post);
             outerDiffData.Items = [];
diff --git a/SabreTools.DatTools/Parser.cs b/SabreTools.DatTools/Parser.cs
index b9134b11..44a64bbc 100644
--- a/SabreTools.DatTools/Parser.cs
+++ b/SabreTools.DatTools/Parser.cs
@@ -94,11 +94,11 @@ namespace SabreTools.DatTools
                 return;
 
             // If the output filename isn't set already, get the internal filename
-            datFile.Header.FileName = string.IsNullOrEmpty(datFile.Header.FileName)
+            datFile.Header.SetFieldValue<string?>(DatHeader.FileNameKey, string.IsNullOrEmpty(datFile.Header.GetFieldValue<string?>(DatHeader.FileNameKey))
                 ? (keepext
                     ? Path.GetFileName(currentPath)
                     : Path.GetFileNameWithoutExtension(currentPath))
-                : datFile.Header.FileName;
+                : datFile.Header.GetFieldValue<string?>(DatHeader.FileNameKey));
 
             // If the output type isn't set already, get the internal output type
             DatFormat currentPathFormat = GetDatFormat(currentPath);
diff --git a/SabreTools.DatTools/Splitter.cs b/SabreTools.DatTools/Splitter.cs
index 4ac661de..bb83d56e 100644
--- a/SabreTools.DatTools/Splitter.cs
+++ b/SabreTools.DatTools/Splitter.cs
@@ -55,12 +55,12 @@ namespace SabreTools.DatTools
 
             // Set all of the appropriate outputs for each of the subsets
             DatFile extADat = DatFile.Create(datFile.Header.CloneStandard());
-            extADat.Header.FileName += $" ({newExtAString})";
+            extADat.Header.SetFieldValue<string?>(DatHeader.FileNameKey, extADat.Header.GetFieldValue<string?>(DatHeader.FileNameKey) + $" ({newExtAString})");
             extADat.Header.SetFieldValue<string?>(Models.Metadata.Header.NameKey, extADat.Header.GetFieldValue<string?>(Models.Metadata.Header.NameKey) + $" ({newExtAString})");
             extADat.Header.SetFieldValue<string?>(Models.Metadata.Header.DescriptionKey, extADat.Header.GetFieldValue<string?>(Models.Metadata.Header.DescriptionKey) + $" ({newExtAString})");
 
             DatFile extBDat = DatFile.Create(datFile.Header.CloneStandard());
-            extBDat.Header.FileName += $" ({newExtBString})";
+            extBDat.Header.SetFieldValue<string?>(DatHeader.FileNameKey, extBDat.Header.GetFieldValue<string?>(DatHeader.FileNameKey) + $" ({newExtBString})");
             extBDat.Header.SetFieldValue<string?>(Models.Metadata.Header.NameKey, extBDat.Header.GetFieldValue<string?>(Models.Metadata.Header.NameKey) + $" ({newExtBString})");
             extBDat.Header.SetFieldValue<string?>(Models.Metadata.Header.DescriptionKey, extBDat.Header.GetFieldValue<string?>(Models.Metadata.Header.DescriptionKey) + $" ({newExtBString})");
 
@@ -123,42 +123,42 @@ namespace SabreTools.DatTools
 
             // TODO: Can this be made into a loop?
             fieldDats[Models.Metadata.Rom.StatusKey] = DatFile.Create(datFile.Header.CloneStandard());
-            fieldDats[Models.Metadata.Rom.StatusKey].Header.FileName += " (Nodump)";
+            fieldDats[Models.Metadata.Rom.StatusKey].Header.SetFieldValue<string?>(DatHeader.FileNameKey, fieldDats[Models.Metadata.Rom.StatusKey].Header.GetFieldValue<string?>(DatHeader.FileNameKey) + " (Nodump)");
             fieldDats[Models.Metadata.Rom.StatusKey].Header.SetFieldValue<string?>(Models.Metadata.Header.NameKey, fieldDats[Models.Metadata.Rom.StatusKey].Header.GetFieldValue<string?>(Models.Metadata.Header.NameKey) + " (Nodump)");
             fieldDats[Models.Metadata.Rom.StatusKey].Header.SetFieldValue<string?>(Models.Metadata.Header.DescriptionKey, fieldDats[Models.Metadata.Rom.StatusKey].Header.GetFieldValue<string?>(Models.Metadata.Header.DescriptionKey) + " (Nodump)");
 
             fieldDats[Models.Metadata.Rom.SHA512Key] = DatFile.Create(datFile.Header.CloneStandard());
-            fieldDats[Models.Metadata.Rom.SHA512Key].Header.FileName += " (SHA-512)";
+            fieldDats[Models.Metadata.Rom.SHA512Key].Header.SetFieldValue<string?>(DatHeader.FileNameKey, fieldDats[Models.Metadata.Rom.SHA512Key].Header.GetFieldValue<string?>(DatHeader.FileNameKey) + " (SHA-512)");
             fieldDats[Models.Metadata.Rom.SHA512Key].Header.SetFieldValue<string?>(Models.Metadata.Header.NameKey, fieldDats[Models.Metadata.Rom.SHA512Key].Header.GetFieldValue<string?>(Models.Metadata.Header.NameKey) + " (SHA-512)");
             fieldDats[Models.Metadata.Rom.SHA512Key].Header.SetFieldValue<string?>(Models.Metadata.Header.DescriptionKey, fieldDats[Models.Metadata.Rom.SHA512Key].Header.GetFieldValue<string?>(Models.Metadata.Header.DescriptionKey) + " (SHA-512)");
 
             fieldDats[Models.Metadata.Rom.SHA384Key] = DatFile.Create(datFile.Header.CloneStandard());
-            fieldDats[Models.Metadata.Rom.SHA384Key].Header.FileName += " (SHA-384)";
+            fieldDats[Models.Metadata.Rom.SHA384Key].Header.SetFieldValue<string?>(DatHeader.FileNameKey, fieldDats[Models.Metadata.Rom.SHA384Key].Header.GetFieldValue<string?>(DatHeader.FileNameKey) + " (SHA-384)");
             fieldDats[Models.Metadata.Rom.SHA384Key].Header.SetFieldValue<string?>(Models.Metadata.Header.NameKey, fieldDats[Models.Metadata.Rom.SHA384Key].Header.GetFieldValue<string?>(Models.Metadata.Header.NameKey) + " (SHA-384)");
             fieldDats[Models.Metadata.Rom.SHA384Key].Header.SetFieldValue<string?>(Models.Metadata.Header.DescriptionKey, fieldDats[Models.Metadata.Rom.SHA384Key].Header.GetFieldValue<string?>(Models.Metadata.Header.DescriptionKey) + " (SHA-384)");
 
             fieldDats[Models.Metadata.Rom.SHA256Key] = DatFile.Create(datFile.Header.CloneStandard());
-            fieldDats[Models.Metadata.Rom.SHA256Key].Header.FileName += " (SHA-256)";
+            fieldDats[Models.Metadata.Rom.SHA256Key].Header.SetFieldValue<string?>(DatHeader.FileNameKey, fieldDats[Models.Metadata.Rom.SHA256Key].Header.GetFieldValue<string?>(DatHeader.FileNameKey) + " (SHA-256)");
             fieldDats[Models.Metadata.Rom.SHA256Key].Header.SetFieldValue<string?>(Models.Metadata.Header.NameKey, fieldDats[Models.Metadata.Rom.SHA256Key].Header.GetFieldValue<string?>(Models.Metadata.Header.NameKey) + " (SHA-256)");
             fieldDats[Models.Metadata.Rom.SHA256Key].Header.SetFieldValue<string?>(Models.Metadata.Header.DescriptionKey, fieldDats[Models.Metadata.Rom.SHA256Key].Header.GetFieldValue<string?>(Models.Metadata.Header.DescriptionKey) + " (SHA-256)");
 
             fieldDats[Models.Metadata.Rom.SHA1Key] = DatFile.Create(datFile.Header.CloneStandard());
-            fieldDats[Models.Metadata.Rom.SHA1Key].Header.FileName += " (SHA-1)";
+            fieldDats[Models.Metadata.Rom.SHA1Key].Header.SetFieldValue<string?>(DatHeader.FileNameKey, fieldDats[Models.Metadata.Rom.SHA1Key].Header.GetFieldValue<string?>(DatHeader.FileNameKey) + " (SHA-1)");
             fieldDats[Models.Metadata.Rom.SHA1Key].Header.SetFieldValue<string?>(Models.Metadata.Header.NameKey, fieldDats[Models.Metadata.Rom.SHA1Key].Header.GetFieldValue<string?>(Models.Metadata.Header.NameKey) + " (SHA-1)");
             fieldDats[Models.Metadata.Rom.SHA1Key].Header.SetFieldValue<string?>(Models.Metadata.Header.DescriptionKey, fieldDats[Models.Metadata.Rom.SHA1Key].Header.GetFieldValue<string?>(Models.Metadata.Header.DescriptionKey) + " (SHA-1)");
 
             fieldDats[Models.Metadata.Rom.MD5Key] = DatFile.Create(datFile.Header.CloneStandard());
-            fieldDats[Models.Metadata.Rom.MD5Key].Header.FileName += " (MD5)";
+            fieldDats[Models.Metadata.Rom.MD5Key].Header.SetFieldValue<string?>(DatHeader.FileNameKey, fieldDats[Models.Metadata.Rom.MD5Key].Header.GetFieldValue<string?>(DatHeader.FileNameKey) + " (MD5)");
             fieldDats[Models.Metadata.Rom.MD5Key].Header.SetFieldValue<string?>(Models.Metadata.Header.NameKey, fieldDats[Models.Metadata.Rom.MD5Key].Header.GetFieldValue<string?>(Models.Metadata.Header.NameKey) + " (MD5)");
             fieldDats[Models.Metadata.Rom.MD5Key].Header.SetFieldValue<string?>(Models.Metadata.Header.DescriptionKey, fieldDats[Models.Metadata.Rom.MD5Key].Header.GetFieldValue<string?>(Models.Metadata.Header.DescriptionKey) + " (MD5)");
 
             fieldDats[Models.Metadata.Rom.CRCKey] = DatFile.Create(datFile.Header.CloneStandard());
-            fieldDats[Models.Metadata.Rom.CRCKey].Header.FileName += " (CRC)";
+            fieldDats[Models.Metadata.Rom.CRCKey].Header.SetFieldValue<string?>(DatHeader.FileNameKey, fieldDats[Models.Metadata.Rom.CRCKey].Header.GetFieldValue<string?>(DatHeader.FileNameKey) + " (CRC)");
             fieldDats[Models.Metadata.Rom.CRCKey].Header.SetFieldValue<string?>(Models.Metadata.Header.NameKey, fieldDats[Models.Metadata.Rom.CRCKey].Header.GetFieldValue<string?>(Models.Metadata.Header.NameKey) + " (CRC)");
             fieldDats[Models.Metadata.Rom.CRCKey].Header.SetFieldValue<string?>(Models.Metadata.Header.DescriptionKey, fieldDats[Models.Metadata.Rom.CRCKey].Header.GetFieldValue<string?>(Models.Metadata.Header.DescriptionKey) + " (CRC)");
 
             fieldDats["null"] = DatFile.Create(datFile.Header.CloneStandard());
-            fieldDats["null"].Header.FileName += " (Other)";
+            fieldDats["null"].Header.SetFieldValue<string?>(DatHeader.FileNameKey, fieldDats["null"].Header.GetFieldValue<string?>(DatHeader.FileNameKey) + " (Other)");
             fieldDats["null"].Header.SetFieldValue<string?>(Models.Metadata.Header.NameKey, fieldDats["null"].Header.GetFieldValue<string?>(Models.Metadata.Header.NameKey) + " (Other)");
             fieldDats["null"].Header.SetFieldValue<string?>(Models.Metadata.Header.DescriptionKey, fieldDats["null"].Header.GetFieldValue<string?>(Models.Metadata.Header.DescriptionKey) + " (Other)");
 
@@ -340,24 +340,28 @@ namespace SabreTools.DatTools
 
             // Now set the new output values
 #if NET20 || NET35
-            newDatFile.Header.FileName = string.IsNullOrEmpty(name)
-                ? datFile.Header.FileName
+            newDatFile.Header.SetFieldValue<string?>(DatHeader.FileNameKey, string.IsNullOrEmpty(name)
+                ? datFile.Header.GetFieldValue<string?>(DatHeader.FileNameKey)
                 : (shortname
                     ? Path.GetFileName(name)
                     : expName
-                    );
+                ));
 #else
-            newDatFile.Header.FileName = WebUtility.HtmlDecode(string.IsNullOrEmpty(name)
-                ? datFile.Header.FileName
+            newDatFile.Header.SetFieldValue<string?>(DatHeader.FileNameKey, WebUtility.HtmlDecode(string.IsNullOrEmpty(name)
+                ? datFile.Header.GetFieldValue<string?>(DatHeader.FileNameKey)
                 : (shortname
                     ? Path.GetFileName(name)
                     : expName
                     )
-                );
+                ));
 #endif
-            newDatFile.Header.FileName = restore ? $"{datFile.Header.FileName} ({newDatFile.Header.FileName})" : newDatFile.Header.FileName;
+            newDatFile.Header.SetFieldValue<string?>(DatHeader.FileNameKey, restore
+                ? $"{datFile.Header.GetFieldValue<string?>(DatHeader.FileNameKey)} ({newDatFile.Header.GetFieldValue<string?>(DatHeader.FileNameKey)})"
+                : newDatFile.Header.GetFieldValue<string?>(DatHeader.FileNameKey));
             newDatFile.Header.SetFieldValue<string?>(Models.Metadata.Header.NameKey, $"{datFile.Header.GetFieldValue<string?>(Models.Metadata.Header.NameKey)} ({expName})");
-            newDatFile.Header.SetFieldValue<string?>(Models.Metadata.Header.NameKey, string.IsNullOrEmpty(datFile.Header.GetFieldValue<string?>(Models.Metadata.Header.DescriptionKey)) ? newDatFile.Header.GetFieldValue<string?>(Models.Metadata.Header.NameKey) : $"{datFile.Header.GetFieldValue<string?>(Models.Metadata.Header.DescriptionKey)} ({expName})");
+            newDatFile.Header.SetFieldValue<string?>(Models.Metadata.Header.NameKey, string.IsNullOrEmpty(datFile.Header.GetFieldValue<string?>(Models.Metadata.Header.DescriptionKey))
+                ? newDatFile.Header.GetFieldValue<string?>(Models.Metadata.Header.NameKey)
+                : $"{datFile.Header.GetFieldValue<string?>(Models.Metadata.Header.DescriptionKey)} ({expName})");
             newDatFile.Header.SetFieldValue<string?>(Models.Metadata.Header.TypeKey, null);
 
             // Write out the temporary DAT to the proper directory
@@ -376,12 +380,12 @@ namespace SabreTools.DatTools
             InternalStopwatch watch = new($"Splitting DAT by size");
 
             DatFile lessThan = DatFile.Create(datFile.Header.CloneStandard());
-            lessThan.Header.FileName += $" (less than {radix})";
+            lessThan.Header.SetFieldValue<string?>(DatHeader.FileNameKey, lessThan.Header.GetFieldValue<string?>(DatHeader.FileNameKey) + $" (less than {radix})");
             lessThan.Header.SetFieldValue<string?>(Models.Metadata.Header.NameKey, lessThan.Header.GetFieldValue<string?>(Models.Metadata.Header.NameKey) + $" (less than {radix})");
             lessThan.Header.SetFieldValue<string?>(Models.Metadata.Header.DescriptionKey, lessThan.Header.GetFieldValue<string?>(Models.Metadata.Header.DescriptionKey) + $" (less than {radix})");
 
             DatFile greaterThan = DatFile.Create(datFile.Header.CloneStandard());
-            greaterThan.Header.FileName += $" (equal-greater than {radix})";
+            greaterThan.Header.SetFieldValue<string?>(DatHeader.FileNameKey, greaterThan.Header.GetFieldValue<string?>(DatHeader.FileNameKey) + $" (equal-greater than {radix})");
             greaterThan.Header.SetFieldValue<string?>(Models.Metadata.Header.NameKey, greaterThan.Header.GetFieldValue<string?>(Models.Metadata.Header.NameKey) + $" (equal-greater than {radix})");
             greaterThan.Header.SetFieldValue<string?>(Models.Metadata.Header.DescriptionKey, greaterThan.Header.GetFieldValue<string?>(Models.Metadata.Header.DescriptionKey) + $" (equal-greater than {radix})");
 
@@ -458,7 +462,7 @@ namespace SabreTools.DatTools
             long currentSize = 0;
             long currentIndex = 0;
             DatFile currentDat = DatFile.Create(datFile.Header.CloneStandard());
-            currentDat.Header.FileName += $"_{currentIndex}";
+            currentDat.Header.SetFieldValue<string?>(DatHeader.FileNameKey, currentDat.Header.GetFieldValue<string?>(DatHeader.FileNameKey) + $"_{currentIndex}");
             currentDat.Header.SetFieldValue<string?>(Models.Metadata.Header.NameKey, currentDat.Header.GetFieldValue<string?>(Models.Metadata.Header.NameKey) + $"_{currentIndex}");
             currentDat.Header.SetFieldValue<string?>(Models.Metadata.Header.DescriptionKey, currentDat.Header.GetFieldValue<string?>(Models.Metadata.Header.DescriptionKey) + $"_{currentIndex}");
 
@@ -501,7 +505,7 @@ namespace SabreTools.DatTools
                     currentSize = 0;
                     currentIndex++;
                     currentDat = DatFile.Create(datFile.Header.CloneStandard());
-                    currentDat.Header.FileName += $"_{currentIndex}";
+                    currentDat.Header.SetFieldValue<string?>(DatHeader.FileNameKey, currentDat.Header.GetFieldValue<string?>(DatHeader.FileNameKey) + $"_{currentIndex}");
                     currentDat.Header.SetFieldValue<string?>(Models.Metadata.Header.NameKey, currentDat.Header.GetFieldValue<string?>(Models.Metadata.Header.NameKey) + $"_{currentIndex}");
                     currentDat.Header.SetFieldValue<string?>(Models.Metadata.Header.DescriptionKey, currentDat.Header.GetFieldValue<string?>(Models.Metadata.Header.DescriptionKey) + $"_{currentIndex}");
                 }
@@ -545,7 +549,7 @@ namespace SabreTools.DatTools
             foreach (ItemType itemType in outputTypes)
             {
                 typeDats[itemType] = DatFile.Create(datFile.Header.CloneStandard());
-                typeDats[itemType].Header.FileName += $" ({itemType})";
+                typeDats[itemType].Header.SetFieldValue<string?>(DatHeader.FileNameKey, typeDats[itemType].Header.GetFieldValue<string?>(DatHeader.FileNameKey) + $" ({itemType})");
                 typeDats[itemType].Header.SetFieldValue<string?>(Models.Metadata.Header.NameKey, typeDats[itemType].Header.GetFieldValue<string?>(Models.Metadata.Header.NameKey) + $" ({itemType})");
                 typeDats[itemType].Header.SetFieldValue<string?>(Models.Metadata.Header.DescriptionKey, typeDats[itemType].Header.GetFieldValue<string?>(Models.Metadata.Header.DescriptionKey) + $" ({itemType})");
             }
diff --git a/SabreTools.DatTools/Statistics.cs b/SabreTools.DatTools/Statistics.cs
index 603bfd92..2054b79f 100644
--- a/SabreTools.DatTools/Statistics.cs
+++ b/SabreTools.DatTools/Statistics.cs
@@ -100,7 +100,7 @@ namespace SabreTools.DatTools
                     DatStatistics individualStats = new()
                     {
                         Statistics = datdata.Items,
-                        DisplayName = datdata.Header.FileName,
+                        DisplayName = datdata.Header.GetFieldValue<string?>(DatHeader.FileNameKey),
                         MachineCount = datdata.Items.Keys.Count,
                         IsDirectory = false,
                     };
diff --git a/SabreTools.DatTools/Verification.cs b/SabreTools.DatTools/Verification.cs
index 7e387815..bad14cd9 100644
--- a/SabreTools.DatTools/Verification.cs
+++ b/SabreTools.DatTools/Verification.cs
@@ -104,7 +104,7 @@ namespace SabreTools.DatTools
             watch.Stop();
 
             // Set fixdat headers in case of writing out
-            datFile.Header.FileName = $"fixDAT_{datFile.Header.FileName}";
+            datFile.Header.SetFieldValue<string?>(DatHeader.FileNameKey, $"fixDAT_{datFile.Header.GetFieldValue<string?>(DatHeader.FileNameKey)}");
             datFile.Header.SetFieldValue<string?>(Models.Metadata.Header.NameKey, $"fixDAT_{datFile.Header.GetFieldValue<string?>(Models.Metadata.Header.NameKey)}");
             datFile.Header.SetFieldValue<string?>(Models.Metadata.Header.DescriptionKey, $"fixDAT_{datFile.Header.GetFieldValue<string?>(Models.Metadata.Header.DescriptionKey)}");
             datFile.Items.ClearMarked();
@@ -153,7 +153,7 @@ namespace SabreTools.DatTools
             watch.Stop();
 
             // Set fixdat headers in case of writing out
-            datFile.Header.FileName = $"fixDAT_{datFile.Header.FileName}";
+            datFile.Header.SetFieldValue<string?>(DatHeader.FileNameKey, $"fixDAT_{datFile.Header.GetFieldValue<string?>(DatHeader.FileNameKey)}");
             datFile.Header.SetFieldValue<string?>(Models.Metadata.Header.NameKey, $"fixDAT_{datFile.Header.GetFieldValue<string?>(Models.Metadata.Header.NameKey)}");
             datFile.Header.SetFieldValue<string?>(Models.Metadata.Header.DescriptionKey, $"fixDAT_{datFile.Header.GetFieldValue<string?>(Models.Metadata.Header.DescriptionKey)}");
             datFile.Items.ClearMarked();
diff --git a/SabreTools.DatTools/Writer.cs b/SabreTools.DatTools/Writer.cs
index d75b13da..ff161b36 100644
--- a/SabreTools.DatTools/Writer.cs
+++ b/SabreTools.DatTools/Writer.cs
@@ -71,7 +71,7 @@ namespace SabreTools.DatTools
             datFile.Items.BucketBy(ItemKey.Machine, DedupeType.None);
 
             // Output the number of items we're going to be writing
-            logger.User($"A total of {datFile.Items.TotalCount - datFile.Items.RemovedCount} items will be written out to '{datFile.Header.FileName}'");
+            logger.User($"A total of {datFile.Items.TotalCount - datFile.Items.RemovedCount} items will be written out to '{datFile.Header.GetFieldValue<string?>(DatHeader.FileNameKey)}'");
 
             // Get the outfile names
             Dictionary<DatFormat, string> outfiles = datFile.Header.CreateOutFileNames(outDir!, overwrite);
@@ -135,7 +135,7 @@ namespace SabreTools.DatTools
                 new()
                 {
                     Statistics = datFile.Items,
-                    DisplayName = datFile.Header.FileName,
+                    DisplayName = datFile.Header.GetFieldValue<string?>(DatHeader.FileNameKey),
                     MachineCount = datFile.Items.Keys.Count,
                     IsDirectory = false,
                 },
@@ -151,30 +151,30 @@ namespace SabreTools.DatTools
         private static void EnsureHeaderFields(DatFile datFile)
         {
             // Empty FileName
-            if (string.IsNullOrEmpty(datFile.Header.FileName))
+            if (string.IsNullOrEmpty(datFile.Header.GetFieldValue<string?>(DatHeader.FileNameKey)))
             {
                 if (string.IsNullOrEmpty(datFile.Header.GetFieldValue<string?>(Models.Metadata.Header.NameKey)) && string.IsNullOrEmpty(datFile.Header.GetFieldValue<string?>(Models.Metadata.Header.DescriptionKey)))
                 {
-                    datFile.Header.FileName = "Default";
+                    datFile.Header.SetFieldValue<string?>(DatHeader.FileNameKey,"Default");
                     datFile.Header.SetFieldValue<string?>(Models.Metadata.Header.NameKey, "Default");
                     datFile.Header.SetFieldValue<string?>(Models.Metadata.Header.DescriptionKey, "Default");
                 }
 
                 else if (string.IsNullOrEmpty(datFile.Header.GetFieldValue<string?>(Models.Metadata.Header.NameKey)) && !string.IsNullOrEmpty(datFile.Header.GetFieldValue<string?>(Models.Metadata.Header.DescriptionKey)))
                 {
-                    datFile.Header.FileName = datFile.Header.GetFieldValue<string?>(Models.Metadata.Header.DescriptionKey);
+                    datFile.Header.SetFieldValue<string?>(DatHeader.FileNameKey,datFile.Header.GetFieldValue<string?>(Models.Metadata.Header.DescriptionKey));
                     datFile.Header.SetFieldValue<string?>(Models.Metadata.Header.NameKey, datFile.Header.GetFieldValue<string?>(Models.Metadata.Header.DescriptionKey));
                 }
 
                 else if (!string.IsNullOrEmpty(datFile.Header.GetFieldValue<string?>(Models.Metadata.Header.NameKey)) && string.IsNullOrEmpty(datFile.Header.GetFieldValue<string?>(Models.Metadata.Header.DescriptionKey)))
                 {
-                    datFile.Header.FileName = datFile.Header.GetFieldValue<string?>(Models.Metadata.Header.NameKey);
+                    datFile.Header.SetFieldValue<string?>(DatHeader.FileNameKey, datFile.Header.GetFieldValue<string?>(Models.Metadata.Header.NameKey));
                     datFile.Header.SetFieldValue<string?>(Models.Metadata.Header.DescriptionKey, datFile.Header.GetFieldValue<string?>(Models.Metadata.Header.NameKey));
                 }
 
                 else if (!string.IsNullOrEmpty(datFile.Header.GetFieldValue<string?>(Models.Metadata.Header.NameKey)) && !string.IsNullOrEmpty(datFile.Header.GetFieldValue<string?>(Models.Metadata.Header.DescriptionKey)))
                 {
-                    datFile.Header.FileName = datFile.Header.GetFieldValue<string?>(Models.Metadata.Header.DescriptionKey);
+                    datFile.Header.SetFieldValue<string?>(DatHeader.FileNameKey, datFile.Header.GetFieldValue<string?>(Models.Metadata.Header.DescriptionKey));
                 }
             }
 
@@ -183,8 +183,8 @@ namespace SabreTools.DatTools
             {
                 if (string.IsNullOrEmpty(datFile.Header.GetFieldValue<string?>(Models.Metadata.Header.NameKey)) && string.IsNullOrEmpty(datFile.Header.GetFieldValue<string?>(Models.Metadata.Header.DescriptionKey)))
                 {
-                    datFile.Header.SetFieldValue<string?>(Models.Metadata.Header.NameKey, datFile.Header.FileName);
-                    datFile.Header.SetFieldValue<string?>(Models.Metadata.Header.DescriptionKey, datFile.Header.FileName);
+                    datFile.Header.SetFieldValue<string?>(Models.Metadata.Header.NameKey, datFile.Header.GetFieldValue<string?>(DatHeader.FileNameKey));
+                    datFile.Header.SetFieldValue<string?>(Models.Metadata.Header.DescriptionKey, datFile.Header.GetFieldValue<string?>(DatHeader.FileNameKey));
                 }
 
                 else if (string.IsNullOrEmpty(datFile.Header.GetFieldValue<string?>(Models.Metadata.Header.NameKey)) && !string.IsNullOrEmpty(datFile.Header.GetFieldValue<string?>(Models.Metadata.Header.DescriptionKey)))
diff --git a/SabreTools.Test/DatFiles/DatHeaderTests.cs b/SabreTools.Test/DatFiles/DatHeaderTests.cs
index b90d2cf5..296befba 100644
--- a/SabreTools.Test/DatFiles/DatHeaderTests.cs
+++ b/SabreTools.Test/DatFiles/DatHeaderTests.cs
@@ -17,8 +17,8 @@ namespace SabreTools.Test.DatFiles
             var datHeader = new DatHeader
             {
                 DatFormat = datFormat,
-                FileName = "test.dat",
             };
+            datHeader.SetFieldValue<string?>(DatHeader.FileNameKey, "test.dat");
 
             // Invoke the method
             string outDir = "C:\\Test";
@@ -37,8 +37,8 @@ namespace SabreTools.Test.DatFiles
             var datHeader = new DatHeader
             {
                 DatFormat = DatFormat.ALL,
-                FileName = "test.dat",
             };
+            datHeader.SetFieldValue<string?>(DatHeader.FileNameKey, "test.dat");
 
             // Invoke the method
             string outDir = "C:\\Test";
diff --git a/SabreTools/Features/BaseFeature.cs b/SabreTools/Features/BaseFeature.cs
index bf9f05e2..95022666 100644
--- a/SabreTools/Features/BaseFeature.cs
+++ b/SabreTools/Features/BaseFeature.cs
@@ -2152,8 +2152,6 @@ Some special strings that can be used:
             // TODO: Sort this by region, like the actual header
             var datHeader = new DatHeader()
             {
-                FileName = GetString(features, FilenameStringValue),
-
                 // Get the depot information
                 InputDepot = new DepotInformation(
                 GetBoolean(features, DepotValue),
@@ -2168,6 +2166,7 @@ Some special strings that can be used:
             datHeader.SetFieldValue<string?>(Models.Metadata.Header.DateKey, GetString(features, DateStringValue));
             datHeader.SetFieldValue<string?>(Models.Metadata.Header.DescriptionKey, GetString(features, DescriptionStringValue));
             datHeader.SetFieldValue<string?>(Models.Metadata.Header.EmailKey, GetString(features, EmailStringValue));
+            datHeader.SetFieldValue<string?>(DatHeader.FileNameKey, GetString(features, FilenameStringValue));
             datHeader.SetFieldValue<MergingFlag>(Models.Metadata.Header.ForceMergingKey, GetString(features, ForceMergingStringValue).AsEnumValue<MergingFlag>());
             datHeader.SetFieldValue<NodumpFlag>(Models.Metadata.Header.ForceNodumpKey, GetString(features, ForceNodumpStringValue).AsEnumValue<NodumpFlag>());
             datHeader.SetFieldValue<PackingFlag>(Models.Metadata.Header.ForceNodumpKey, GetString(features, ForcePackingStringValue).AsEnumValue<PackingFlag>());
diff --git a/SabreTools/Features/Sort.cs b/SabreTools/Features/Sort.cs
index 09dcaccb..e8b99c37 100644
--- a/SabreTools/Features/Sort.cs
+++ b/SabreTools/Features/Sort.cs
@@ -108,14 +108,14 @@ namespace SabreTools.Features
                     // If we have the depot flag, respect it
                     bool success;
                     if (Header.InputDepot?.IsActive ?? false)
-                        success = Rebuilder.RebuildDepot(datdata, Inputs, Path.Combine(OutputDir!, datdata.Header.FileName!), date, delete, inverse, outputFormat);
+                        success = Rebuilder.RebuildDepot(datdata, Inputs, Path.Combine(OutputDir!, datdata.Header.GetFieldValue<string?>(DatHeader.FileNameKey)!), date, delete, inverse, outputFormat);
                     else
-                        success = Rebuilder.RebuildGeneric(datdata, Inputs, Path.Combine(OutputDir!, datdata.Header.FileName!), quickScan, date, delete, inverse, outputFormat, asFiles);
+                        success = Rebuilder.RebuildGeneric(datdata, Inputs, Path.Combine(OutputDir!, datdata.Header.GetFieldValue<string?>(DatHeader.FileNameKey)!), quickScan, date, delete, inverse, outputFormat, asFiles);
 
                     // If we have a success and we're updating the DAT, write it out
                     if (success && updateDat)
                     {
-                        datdata.Header.FileName = $"fixDAT_{Header.FileName}";
+                        datdata.Header.SetFieldValue<string?>(DatHeader.FileNameKey, $"fixDAT_{Header.GetFieldValue<string?>(DatHeader.FileNameKey)}");
                         datdata.Header.SetFieldValue<string?>(Models.Metadata.Header.NameKey, $"fixDAT_{Header.GetFieldValue<string?>(Models.Metadata.Header.NameKey)}");
                         datdata.Header.SetFieldValue<string?>(Models.Metadata.Header.DescriptionKey, $"fixDAT_{Header.GetFieldValue<string?>(Models.Metadata.Header.DescriptionKey)}");
                         datdata.Items.ClearMarked();
@@ -156,7 +156,7 @@ namespace SabreTools.Features
                 // If we have a success and we're updating the DAT, write it out
                 if (success && updateDat)
                 {
-                    datdata.Header.FileName = $"fixDAT_{Header.FileName}";
+                    datdata.Header.SetFieldValue<string?>(DatHeader.FileNameKey, $"fixDAT_{Header.GetFieldValue<string?>(DatHeader.FileNameKey)}");
                     datdata.Header.SetFieldValue<string?>(Models.Metadata.Header.NameKey, $"fixDAT_{Header.GetFieldValue<string?>(Models.Metadata.Header.NameKey)}");
                     datdata.Header.SetFieldValue<string?>(Models.Metadata.Header.DescriptionKey, $"fixDAT_{Header.GetFieldValue<string?>(Models.Metadata.Header.DescriptionKey)}");
                     datdata.Items.ClearMarked();
diff --git a/SabreTools/Features/Stats.cs b/SabreTools/Features/Stats.cs
index 34c2144a..24dffdf5 100644
--- a/SabreTools/Features/Stats.cs
+++ b/SabreTools/Features/Stats.cs
@@ -49,7 +49,7 @@ The stats that are outputted are as follows:
             if (!base.ProcessFeatures(features))
                 return false;
 
-            string filename = Header!.FileName!;
+            string filename = Header!.GetFieldValue<string?>(DatFiles.DatHeader.FileNameKey)!;
             if (Path.GetFileName(filename) != filename)
             {
                 if (string.IsNullOrWhiteSpace(OutputDir))
diff --git a/SabreTools/Features/Update.cs b/SabreTools/Features/Update.cs
index 2492c0ab..800b11b0 100644
--- a/SabreTools/Features/Update.cs
+++ b/SabreTools/Features/Update.cs
@@ -289,7 +289,7 @@ namespace SabreTools.Features
                         string innerpost = $" ({j} - {inputPaths[j].GetNormalizedFileName(true)} Only)";
 
                         datHeaders[j] = userInputDat.Header;
-                        datHeaders[j].FileName += innerpost;
+                        datHeaders[j].SetFieldValue<string?>(DatHeader.FileNameKey, datHeaders[j].GetFieldValue<string?>(DatHeader.FileNameKey) + innerpost);
                         datHeaders[j].SetFieldValue<string?>(Models.Metadata.Header.NameKey, datHeaders[j].GetFieldValue<string?>(Models.Metadata.Header.NameKey) + innerpost);
                         datHeaders[j].SetFieldValue<string?>(Models.Metadata.Header.DescriptionKey, datHeaders[j].GetFieldValue<string?>(Models.Metadata.Header.DescriptionKey) + innerpost);
                     }