diff --git a/SabreTools.Library/DatItems/DipSwitch.cs b/SabreTools.Library/DatItems/DipSwitch.cs
index f39a0152..9f56f6fd 100644
--- a/SabreTools.Library/DatItems/DipSwitch.cs
+++ b/SabreTools.Library/DatItems/DipSwitch.cs
@@ -350,7 +350,7 @@ namespace SabreTools.Library.DatItems
             #region SoftwareList
 
             // Filter on Part
-            if (Part != null)
+            if (PartSpecified)
             {
                 if (!Part.PassesFilter(filter))
                     return false;
diff --git a/SabreTools.Library/DatItems/Disk.cs b/SabreTools.Library/DatItems/Disk.cs
index 95f0d1d1..bbcd8ef6 100644
--- a/SabreTools.Library/DatItems/Disk.cs
+++ b/SabreTools.Library/DatItems/Disk.cs
@@ -491,14 +491,14 @@ namespace SabreTools.Library.DatItems
             #region SoftwareList
 
             // Filter on DiskArea
-            if (DiskArea != null)
+            if (DiskAreaSpecified)
             {
                 if (!DiskArea.PassesFilter(filter))
                     return false;
             }
 
             // Filter on Part
-            if (Part != null)
+            if (PartSpecified)
             {
                 if (!Part.PassesFilter(filter))
                     return false;
diff --git a/SabreTools.Library/DatItems/Rom.cs b/SabreTools.Library/DatItems/Rom.cs
index cd4a6696..0d588d63 100644
--- a/SabreTools.Library/DatItems/Rom.cs
+++ b/SabreTools.Library/DatItems/Rom.cs
@@ -941,14 +941,14 @@ namespace SabreTools.Library.DatItems
                 return false;
 
             // Filter on DataArea
-            if (DataArea != null)
+            if (DataAreaSpecified)
             {
                 if (!DataArea.PassesFilter(filter))
                     return false;
             }
 
             // Filter on Part
-            if (Part != null)
+            if (PartSpecified)
             {
                 if (!Part.PassesFilter(filter))
                     return false;