diff --git a/src/BizHawk.BizInvoke/BizInvoker.cs b/src/BizHawk.BizInvoke/BizInvoker.cs
index 85681491b3..59d4844a2c 100644
--- a/src/BizHawk.BizInvoke/BizInvoker.cs
+++ b/src/BizHawk.BizInvoke/BizInvoker.cs
@@ -49,11 +49,17 @@ namespace BizHawk.BizInvoke
 		/// </summary>
 		private static readonly ModuleBuilder ImplModuleBuilder;
 
+		/// <summary>
+		/// How far into a class pointer the first field is.  Different on mono and fw.
+		/// </summary>
+		private static readonly int ClassFieldOffset;
+
 		static BizInvoker()
 		{
 			var aname = new AssemblyName("BizInvokeProxyAssembly");
 			ImplAssemblyBuilder = AppDomain.CurrentDomain.DefineDynamicAssembly(aname, AssemblyBuilderAccess.Run);
 			ImplModuleBuilder = ImplAssemblyBuilder.DefineDynamicModule("BizInvokerModule");
+			ClassFieldOffset = BizInvokerUtilities.ComputeClassFieldOffset();
 		}
 
 		/// <summary>
@@ -476,6 +482,7 @@ namespace BizHawk.BizInvoke
 
 			if (typeof(Delegate).IsAssignableFrom(type))
 			{
+				// callback -- use the same callingconventionadapter on it that the invoker is being made from
 				var mi = typeof(ICallingConventionAdapter).GetMethod("GetFunctionPointerForDelegate");
 				var end = il.DefineLabel();
 				var isNull = il.DefineLabel();
@@ -515,7 +522,7 @@ namespace BizHawk.BizInvoke
 				il.Emit(OpCodes.Stloc, loc);
 				il.Emit(OpCodes.Conv_I);
 				// skip past the methodtable pointer to the first field
-				il.Emit(IntPtr.Size == 4 ? OpCodes.Ldc_I4_4 : OpCodes.Ldc_I4_8);
+				il.Emit(OpCodes.Ldc_I4, ClassFieldOffset);
 				il.Emit(OpCodes.Conv_I);
 				il.Emit(OpCodes.Add);
 				il.Emit(OpCodes.Br, end);
diff --git a/src/BizHawk.BizInvoke/BizInvokerUtilities.cs b/src/BizHawk.BizInvoke/BizInvokerUtilities.cs
new file mode 100644
index 0000000000..a07a40df86
--- /dev/null
+++ b/src/BizHawk.BizInvoke/BizInvokerUtilities.cs
@@ -0,0 +1,48 @@
+using System;
+using System.Runtime.InteropServices;
+
+namespace BizHawk.BizInvoke
+{
+	public static unsafe class BizInvokerUtilities
+	{
+		[StructLayout(LayoutKind.Explicit)]
+		private class U
+		{
+			[FieldOffset(0)]
+			public U1 First;
+			[FieldOffset(0)]
+			public U2 Second;
+		}
+		[StructLayout(LayoutKind.Explicit)]
+		private class U1
+		{
+			[FieldOffset(0)]
+			public UIntPtr P;
+		}
+		[StructLayout(LayoutKind.Explicit)]
+		private class U2
+		{
+			[FieldOffset(0)]
+			public CF Target;
+		}
+		private class CF
+		{
+			public int FirstField;
+		}
+		/// <summary>
+		/// Didn't I have code somewhere else to do this already?
+		/// </summary>
+		/// <returns></returns>
+		public static unsafe int ComputeClassFieldOffset()
+		{
+			var c = new CF();
+			int ret;
+			fixed(int* fx = &c.FirstField)
+			{
+				var u = new U { Second = new U2 { Target = c }};
+				ret = (int)((ulong)(UIntPtr)fx - (ulong)u.First.P);
+			}
+			return ret;
+		}
+	}
+}
diff --git a/src/BizHawk.Emulation.Cores/Waterbox/Syscalls/Syscalls.cs b/src/BizHawk.Emulation.Cores/Waterbox/Syscalls/Syscalls.cs
index 1ed67b4bba..cf3b9e51c3 100644
--- a/src/BizHawk.Emulation.Cores/Waterbox/Syscalls/Syscalls.cs
+++ b/src/BizHawk.Emulation.Cores/Waterbox/Syscalls/Syscalls.cs
@@ -394,17 +394,17 @@ namespace BizHawk.Emulation.Cores.Waterbox
 		}
 
 		[StructLayout(LayoutKind.Sequential)]
-		public class TimeSpec
+		public struct TimeSpec
 		{
 			public long Seconds;
 			public long NanoSeconds;
 		}
 
 		[BizExport(CallingConvention.Cdecl, EntryPoint = "__wsyscalltab[228]")]
-		public int SysClockGetTime(int which, [In, Out] TimeSpec time)
+		public unsafe int SysClockGetTime(int which, TimeSpec* time)
 		{
-			time.Seconds = 1495889068;
-			time.NanoSeconds = 0;
+			time->Seconds = 1495889068;
+			time->NanoSeconds = 0;
 			return 0;
 		}