diff --git a/SabreTools.Serialization/Models/Atari7800/Header.cs b/SabreTools.Serialization/Models/Atari7800/Header.cs
index a99cabea..e3dfb86e 100644
--- a/SabreTools.Serialization/Models/Atari7800/Header.cs
+++ b/SabreTools.Serialization/Models/Atari7800/Header.cs
@@ -32,8 +32,8 @@ namespace SabreTools.Data.Models.Atari7800
         /// Endianness possibly varies by version?
         /// Version 1 - Big-endian
         /// Version 2 - ?????
-        /// Version 3 - ?????
-        /// Version 4 - ?????
+        /// Version 3 - Documented as little-endian (unconfirmed)
+        /// Version 4 - Documented as little-endian (unconfirmed)
         /// </remarks>
         public uint RomSizeWithoutHeader { get; set; }
 
diff --git a/SabreTools.Serialization/Readers/Atari7800Cart.cs b/SabreTools.Serialization/Readers/Atari7800Cart.cs
index 2720cf69..81a23881 100644
--- a/SabreTools.Serialization/Readers/Atari7800Cart.cs
+++ b/SabreTools.Serialization/Readers/Atari7800Cart.cs
@@ -66,7 +66,11 @@ namespace SabreTools.Serialization.Readers
             obj.HeaderVersion = data.ReadByteValue();
             obj.MagicText = data.ReadBytes(16);
             obj.CartTitle = data.ReadBytes(32);
-            obj.RomSizeWithoutHeader = data.ReadUInt32BigEndian();
+            if (obj.HeaderVersion == 1)
+                obj.RomSizeWithoutHeader = data.ReadUInt32BigEndian();
+            else
+                obj.RomSizeWithoutHeader = data.ReadUInt32LittleEndian();
+
             obj.CartType = (CartType)data.ReadUInt16LittleEndian();
             obj.Controller1Type = (ControllerType)data.ReadByteValue();
             obj.Controller2Type = (ControllerType)data.ReadByteValue();