Use 'ref', not 'out', for passing arguments to a method parameter declared as "[In, Out] ref".

ICSharpCode.Decompiler/Ast/AstMethodBodyBuilder.cs

@@ -1012,7 +1012,8 @@ namespace ICSharpCode.Decompiler.Ast
 			// Convert 'ref' into 'out' where necessary
 			for (int i = 0; i < methodArgs.Count && i < cecilMethod.Parameters.Count; i++) {
 				DirectionExpression dir = methodArgs[i] as DirectionExpression;
-				if (dir != null && cecilMethod.Parameters[i].IsOut)
+				ParameterDefinition p = cecilMethod.Parameters[i];
+				if (dir != null && p.IsOut && !p.IsIn)
 					dir.FieldDirection = FieldDirection.Out;
 			}
 		}

ICSharpCode.Decompiler/Tests/PInvoke.cs

@@ -84,4 +84,13 @@ public class PInvoke
 	public void CustomMarshal2([MarshalAs(UnmanagedType.CustomMarshaler, MarshalType = "MyCompany.MyMarshaler", MarshalCookie = "Cookie")] object o)
 	{
 	}
+	
+	[DllImport("ws2_32.dll", SetLastError = true)]
+	internal static extern IntPtr ioctlsocket([In] IntPtr socketHandle, [In] int cmd, [In] [Out] ref int argp);
+	
+	public void CallMethodWithInOutParameter()
+	{
+		int num = 0;
+		PInvoke.ioctlsocket(IntPtr.Zero, 0, ref num);
+	}
 }