diff -r 567bb019e3e3 -r 7e817e7e631c gstreamer_core/gst/gstinterface.c
--- a/gstreamer_core/gst/gstinterface.c	Tue Aug 31 15:30:33 2010 +0300
+++ b/gstreamer_core/gst/gstinterface.c	Wed Sep 01 12:16:41 2010 +0100
@@ -51,10 +51,9 @@
 GType
 gst_implements_interface_get_type (void)
 {
-  static volatile gsize gst_interface_type = 0;
+  static GType gst_interface_type = 0;
 
-  if (g_once_init_enter (&gst_interface_type)) {
-    GType _type;
+  if (!gst_interface_type) {
     static const GTypeInfo gst_interface_info = {
       sizeof (GstImplementsInterfaceClass),
       (GBaseInitFunc) gst_implements_interface_class_init,
@@ -68,11 +67,10 @@
       NULL
     };
 
-    _type = g_type_register_static (G_TYPE_INTERFACE,
+    gst_interface_type = g_type_register_static (G_TYPE_INTERFACE,
         "GstImplementsInterface", &gst_interface_info, 0);
 
-    g_type_interface_add_prerequisite (_type, GST_TYPE_ELEMENT);
-    g_once_init_leave (&gst_interface_type, _type);
+    g_type_interface_add_prerequisite (gst_interface_type, GST_TYPE_ELEMENT);
   }
 
   return gst_interface_type;
@@ -190,11 +188,15 @@
 gboolean
 gst_implements_interface_check (gpointer from, GType type)
 {
+  GstImplementsInterface *iface;
+
   /* check cast, return FALSE if it fails, don't give a warning... */
   if (!G_TYPE_CHECK_INSTANCE_TYPE (from, type)) {
     return FALSE;
   }
 
+  iface = G_TYPE_CHECK_INSTANCE_CAST (from, type, GstImplementsInterface);
+
   /* now, if we're an element (or derivative), is this thing
    * actually implemented for real? */
   if (GST_IS_ELEMENT (from)) {