diff --git a/SabreTools.Serialization/Models/XZ/Block.cs b/SabreTools.Serialization/Models/XZ/Block.cs
index 590efefc..904637a2 100644
--- a/SabreTools.Serialization/Models/XZ/Block.cs
+++ b/SabreTools.Serialization/Models/XZ/Block.cs
@@ -24,14 +24,14 @@ namespace SabreTools.Data.Models.XZ
         /// Present if <see cref="BlockFlags.CompressedSize"/> is set. 
         /// </summary>
         /// <remarks>Stored as a variable-length integer</remarks>
-        public byte[]? CompressedSize { get; set; }
+        public ulong CompressedSize { get; set; }
 
         /// <summary>
         /// Size of the block after decompression
         /// Present if <see cref="BlockFlags.UncompressedSize"/> is set. 
         /// </summary>
         /// <remarks>Stored as a variable-length integer</remarks>
-        public byte[]? UncompressedSize { get; set; }
+        public ulong UncompressedSize { get; set; }
 
         /// <summary>
         /// List of filter flags
diff --git a/SabreTools.Serialization/Models/XZ/FilterFlags.cs b/SabreTools.Serialization/Models/XZ/FilterFlags.cs
index e6216884..170437b6 100644
--- a/SabreTools.Serialization/Models/XZ/FilterFlags.cs
+++ b/SabreTools.Serialization/Models/XZ/FilterFlags.cs
@@ -6,13 +6,13 @@ namespace SabreTools.Data.Models.XZ
         /// Filter ID
         /// </summary>
         /// <remarks>Stored as a variable-length integer</remarks>
-        public byte[]? FilterID { get; set; }
+        public ulong FilterID { get; set; }
 
         /// <summary>
         /// Filter ID
         /// </summary>
         /// <remarks>Stored as a variable-length integer</remarks>
-        public byte[]? SizeOfProperties { get; set; }
+        public ulong SizeOfProperties { get; set; }
 
         /// <summary>
         /// Properties of the filter whose length is given by
diff --git a/SabreTools.Serialization/Models/XZ/Index.cs b/SabreTools.Serialization/Models/XZ/Index.cs
index 094f1480..53bf1fae 100644
--- a/SabreTools.Serialization/Models/XZ/Index.cs
+++ b/SabreTools.Serialization/Models/XZ/Index.cs
@@ -13,7 +13,7 @@ namespace SabreTools.Data.Models.XZ
         /// Stream
         /// </summary>
         /// <remarks>Stored as a variable-length integer</remarks>
-        public byte[]? NumberOfRecords { get; set; }
+        public ulong NumberOfRecords { get; set; }
 
         /// <summary>
         /// One record per block
diff --git a/SabreTools.Serialization/Models/XZ/Record.cs b/SabreTools.Serialization/Models/XZ/Record.cs
index f25c1944..64b60c3c 100644
--- a/SabreTools.Serialization/Models/XZ/Record.cs
+++ b/SabreTools.Serialization/Models/XZ/Record.cs
@@ -6,12 +6,12 @@ namespace SabreTools.Data.Models.XZ
         /// Unpadded size of the block
         /// </summary>
         /// <remarks>Stored as a variable-length integer</remarks>
-        public byte[]? UnpaddedSize { get; set; }
+        public ulong UnpaddedSize { get; set; }
 
         /// <summary>
         /// Uncompressed size of the block
         /// </summary>
         /// <remarks>Stored as a variable-length integer</remarks>
-        public byte[]? NumberOfRecords { get; set; }
+        public ulong NumberOfRecords { get; set; }
     }
 }