diff --git a/ChangeLog b/ChangeLog
index 7adbfa13b..051b6fa2e 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,10 @@
+2008-12-22  Andrés G. Aragoneses  <aaragoneses@novell.com>
+
+	* generator/InterfaceGen.cs: track API.
+	* glib/GType.cs: simplify, avoiding a static method.
+	* glib/Value.cs: reuse g_type_is_a.
+	[Improves fix for #448009 in r121990]
+
 2008-12-22  Andrés G. Aragoneses  <aaragoneses@novell.com>
 
 	* generator/InterfaceGen.cs: use the new GLib API to detect
diff --git a/generator/InterfaceGen.cs b/generator/InterfaceGen.cs
index 763fb57ce..84042c50d 100644
--- a/generator/InterfaceGen.cs
+++ b/generator/InterfaceGen.cs
@@ -177,7 +177,7 @@ namespace GtkSharp.Generation {
 			sw.WriteLine ();
 			sw.WriteLine ("\t\tpublic " + Name + "Adapter (IntPtr handle)");
 			sw.WriteLine ("\t\t{");
-			sw.WriteLine ("\t\t\tif (!GLib.GType.IsInstance (handle, _gtype))");
+			sw.WriteLine ("\t\t\tif (!_gtype.IsInstance (handle))");
 			sw.WriteLine ("\t\t\t\tthrow new ArgumentException (\"The gobject doesn't implement the GInterface of this adapter\", \"handle\");");
 			sw.WriteLine ("\t\t\tthis.handle = handle;");
 			sw.WriteLine ("\t\t}");
diff --git a/glib/GType.cs b/glib/GType.cs
index 1c1f7dcf9..4455a8e00 100755
--- a/glib/GType.cs
+++ b/glib/GType.cs
@@ -339,9 +339,9 @@ namespace GLib {
 			return g_type_is_a (type, is_a_type.Val);
 		}
 
-		public static bool IsInstance (IntPtr raw, GType type)
+		public bool IsInstance (IntPtr raw)
 		{
-			return GType.Is (ValFromInstancePtr (raw), type);
+			return GType.Is (ValFromInstancePtr (raw), this);
 		}
 
 		[DllImport("libgobject-2.0-0.dll")]
diff --git a/glib/Value.cs b/glib/Value.cs
index bdc26ed76..d8954b856 100755
--- a/glib/Value.cs
+++ b/glib/Value.cs
@@ -351,8 +351,8 @@ namespace GLib {
 					return (long) this;
 				else if (type == GType.UInt64.Val)
 					return (ulong) this;
-				else if (g_type_is_a (type, GType.Enum.Val) ||
-					 g_type_is_a (type, GType.Flags.Val))
+				else if (GType.Is (type, GType.Enum) ||
+					 GType.Is (type, GType.Flags))
 					return (Enum) this;
 				else if (type == GType.Float.Val)
 					return (float) this;
@@ -366,9 +366,9 @@ namespace GLib {
 					return g_value_get_param (ref this);
 				else if (type == ManagedValue.GType.Val)
 					return ManagedValue.ObjectForWrapper (g_value_get_boxed (ref this));
-				else if (g_type_is_a (type, GType.Object.Val))
+				else if (GType.Is (type, GType.Object))
 					return (GLib.Object) this;
-				else if (g_type_is_a (type, GType.Boxed.Val))
+				else if (GType.Is (type, GType.Boxed))
 					return ToBoxed ();
 				else if (type == IntPtr.Zero)
 					return null;
@@ -390,9 +390,9 @@ namespace GLib {
 					g_value_set_int64 (ref this, (long) value);
 				else if (type == GType.UInt64.Val)
 					g_value_set_uint64 (ref this, (ulong) value);
-				else if (g_type_is_a (type, GType.Enum.Val))
+				else if (GType.Is (type, GType.Enum))
 					g_value_set_enum (ref this, (int)value);
-				else if (g_type_is_a (type, GType.Flags.Val))
+				else if (GType.Is (type, GType.Flags))
 					g_value_set_flags (ref this, (uint)(int)value);
 				else if (type == GType.Float.Val)
 					g_value_set_float (ref this, (float) value);
@@ -419,12 +419,12 @@ namespace GLib {
 					IntPtr wrapper = ManagedValue.WrapObject (value);
 					g_value_set_boxed (ref this, wrapper);
 					ManagedValue.ReleaseWrapper (wrapper);
-				} else if (g_type_is_a (type, GType.Object.Val))
+				} else if (GType.Is (type, GType.Object))
 					if(value is GLib.Object)
 						g_value_set_object (ref this, (value as GLib.Object).Handle);
 					else
 						g_value_set_object (ref this, (value as GLib.GInterfaceAdapter).Handle);
-				else if (g_type_is_a (type, GType.Boxed.Val)) {
+				else if (GType.Is (type, GType.Boxed)) {
 					if (value is IWrapper) {
 						g_value_set_boxed (ref this, ((IWrapper)value).Handle);
 						return;
@@ -439,7 +439,7 @@ namespace GLib {
 
 		internal void Update (object val)
 		{
-			if (g_type_is_a (type, GType.Boxed.Val) && !(val is IWrapper))
+			if (GType.Is (type, GType.Boxed) && !(val is IWrapper))
 				Marshal.StructureToPtr (val, g_value_get_boxed (ref this), false);
 		}
 
@@ -567,9 +567,6 @@ namespace GLib {
 		[DllImport("libgobject-2.0-0.dll")]
 		static extern uint g_value_get_flags (ref Value val);
 
-		[DllImport("libgobject-2.0-0.dll")]
-		static extern bool g_type_is_a (IntPtr type, IntPtr is_a_type);
-
 		[DllImport("libgobject-2.0-0.dll")]
 		static extern IntPtr g_strv_get_type ();
 	}