diff --git a/generator/Signature.cs b/generator/Signature.cs
index 156480003..9f64ae3b8 100644
--- a/generator/Signature.cs
+++ b/generator/Signature.cs
@@ -150,7 +150,7 @@ namespace GtkSharp.Generation {
 				result [i] = p.PassAs != "" ? p.PassAs + " " : "";
 				if (p.IsOptional && p.PassAs == String.Empty) {
 					if (p.Generatable is StructGen || p.Generatable is BoxedGen)
-						result [i++] += " .Zero";
+						result [i++] += p.CSType + ".Zero";
 					else if (p.CSType == "System.IntPtr")
 						result [i++] += "System.IntPtr.Zero";
 					else