diff --git a/ChangeLog b/ChangeLog
index 59134364a..bb78fcfbe 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,9 @@
+2005-08-22  Dan Winship  <danw@novell.com>
+
+	* generator/CallbackGen.cs (Validate, MarshalType): if validation
+	fails, set MarshalType to "" to propagate that failure into
+	methods that have args of this type. [Fixes #75851]
+
 2005-08-15  Peter Williams  <peter@newton.cx>
 
 	* bootstrap-generic: New script, handles bootstrapping stuff generically
diff --git a/generator/CallbackGen.cs b/generator/CallbackGen.cs
index a211b19ef..4e667b7d4 100644
--- a/generator/CallbackGen.cs
+++ b/generator/CallbackGen.cs
@@ -31,6 +31,7 @@ namespace GtkSharp.Generation {
 		private Signature sig = null;
 		private ImportSignature isig = null;
 		private ReturnValue retval;
+		private bool valid = true;
 
 		public CallbackGen (XmlElement ns, XmlElement elem) : base (ns, elem) 
 		{
@@ -44,21 +45,27 @@ namespace GtkSharp.Generation {
 			if (!retval.Validate ()) {
 				Console.WriteLine ("rettype: " + retval.CType + " in callback " + CName);
 				Statistics.ThrottledCount++;
+				valid = false;
 				return false;
 			}
 
 			if (!parms.Validate ()) {
 				Console.WriteLine (" in callback " + CName);
 				Statistics.ThrottledCount++;
+				valid = false;
 				return false;
 			}
 
+			valid = true;
 			return true;
 		}
 
 		public override string MarshalType {
 			get {
-				return NS + "Sharp." + Name + "Native";
+				if (valid)
+					return NS + "Sharp." + Name + "Native";
+				else
+					return "";
 			}
 		}