diff --git a/BizHawk.Emulation.Cores/Consoles/Nintendo/NES/Boards/GxROM.cs b/BizHawk.Emulation.Cores/Consoles/Nintendo/NES/Boards/GxROM.cs
index a353722067..699abea7c3 100644
--- a/BizHawk.Emulation.Cores/Consoles/Nintendo/NES/Boards/GxROM.cs
+++ b/BizHawk.Emulation.Cores/Consoles/Nintendo/NES/Boards/GxROM.cs
@@ -71,7 +71,7 @@ namespace BizHawk.Emulation.Cores.Nintendo.NES
 
 		public override void WritePRG(int addr, byte value)
 		{
-			chr = ((value & 3) & chr_mask);
+			chr = ((value & 7) & chr_mask);
 			prg = (((value>>4) & 3) & prg_mask);
 		}
 
@@ -82,4 +82,4 @@ namespace BizHawk.Emulation.Cores.Nintendo.NES
 			ser.Sync("prg", ref prg);
 		}
 	}
-}
\ No newline at end of file
+}