diff --git a/BizHawk.Common/BizInvoke/BizInvoker.cs b/BizHawk.Common/BizInvoke/BizInvoker.cs
index 427ad293ad..609714d587 100644
--- a/BizHawk.Common/BizInvoke/BizInvoker.cs
+++ b/BizHawk.Common/BizInvoke/BizInvoker.cs
@@ -309,7 +309,10 @@ namespace BizHawk.Common.BizInvoke
 
 			il.Emit(OpCodes.Ldarg_0);
 			il.Emit(OpCodes.Ldfld, field);
-			il.EmitCalli(OpCodes.Calli, nativeCall, returnType, nativeParamTypes.ToArray());
+			il.EmitCalli(OpCodes.Calli, 
+				nativeCall, 
+				returnType == typeof(bool) ? typeof(byte) : returnType, // undo winapi style bool garbage
+				nativeParamTypes.ToArray());
 
 			if (monitorField != null) // monitor: finally exit
 			{