diff --git a/BizHawk.Emulation/Computers/Commodore64/C64.cs b/BizHawk.Emulation/Computers/Commodore64/C64.cs
index 0518962806..3abaf0881a 100644
--- a/BizHawk.Emulation/Computers/Commodore64/C64.cs
+++ b/BizHawk.Emulation/Computers/Commodore64/C64.cs
@@ -9,7 +9,7 @@ namespace BizHawk.Emulation.Computers.Commodore64
 {
 	public partial class  C64 : IEmulator
 	{
-		public C64(GameInfo game, byte[] rom)
+		public C64(GameInfo game, byte[] rom, string romextension)
 		{
 			videoProvider = new MyVideoProvider(this);
 			SetupMemoryDomains();
diff --git a/BizHawk.MultiClient/MainForm.cs b/BizHawk.MultiClient/MainForm.cs
index b9ab2621bd..b450530fc8 100644
--- a/BizHawk.MultiClient/MainForm.cs
+++ b/BizHawk.MultiClient/MainForm.cs
@@ -1646,7 +1646,7 @@ namespace BizHawk.MultiClient
 								nextEmulator = a78;
 								break;
 							case "C64":
-								C64 c64 = new C64(game, rom.RomData); //TODO: need to load in BIOSes?
+								C64 c64 = new C64(game, rom.RomData, rom.Extension); //TODO: need to load in BIOSes?
 								nextEmulator = c64;
 								break;
 						}
diff --git a/BizHawk.MultiClient/RomGame.cs b/BizHawk.MultiClient/RomGame.cs
index 0a4dd67ae8..632a09664c 100644
--- a/BizHawk.MultiClient/RomGame.cs
+++ b/BizHawk.MultiClient/RomGame.cs
@@ -8,6 +8,7 @@ namespace BizHawk.MultiClient
 		public byte[] RomData;
 		public byte[] FileData;
 		public GameInfo GameInfo;
+		public string Extension;
 
 		private const int BankSize = 1024;
 
@@ -22,7 +23,7 @@ namespace BizHawk.MultiClient
 
 			var stream = file.GetStream();
 			FileData = Util.ReadAllBytes(stream);
-
+			Extension = file.Extension;
 			// if we're offset exactly 512 bytes from a 1024-byte boundary, 
 			// assume we have a header of that size. Otherwise, assume it's just all rom.
 			// Other 'recognized' header sizes may need to be added.