diff --git a/SabreTools.Models/GZIP/ExtraFieldData.cs b/SabreTools.Models/GZIP/ExtraFieldData.cs
index d310e3a..10f72ed 100644
--- a/SabreTools.Models/GZIP/ExtraFieldData.cs
+++ b/SabreTools.Models/GZIP/ExtraFieldData.cs
@@ -7,13 +7,13 @@ namespace SabreTools.Models.GZIP
         /// SI1 and SI2 provide a subfield ID, typically two ASCII letters
         /// with some mnemonic value.
         /// </summary>
-        public byte SI1 { get; set; }
+        public byte SubfieldID1 { get; set; }
 
         /// <summary>
         /// SI1 and SI2 provide a subfield ID, typically two ASCII letters
         /// with some mnemonic value.
         /// </summary>
-        public byte SI2 { get; set; }
+        public byte SubfieldID2 { get; set; }
 
         /// <summary>
         /// LEN gives the length of the subfield data, excluding the 4