diff --git a/gobject/gtype.h b/gobject/gtype.h
index 6348833a2..d10de00cd 100644
--- a/gobject/gtype.h
+++ b/gobject/gtype.h
@@ -2501,15 +2501,16 @@ const gchar *    g_type_name_from_class         (GTypeClass	*g_class);
 
 
 /* --- implementation bits --- */
-#ifndef G_DISABLE_CAST_CHECKS
+#if (defined(G_DISABLE_CAST_CHECKS) && G_DISABLE_CAST_CHECKS != 0) || (!defined(G_DISABLE_CAST_CHECKS) && defined(__OPTIMIZE__))
+#  define _G_TYPE_CIC(ip, gt, ct)       ((ct*) ip)
+#  define _G_TYPE_CCC(cp, gt, ct)       ((ct*) cp)
+#else
 #  define _G_TYPE_CIC(ip, gt, ct) \
     ((ct*) (void *) g_type_check_instance_cast ((GTypeInstance*) ip, gt))
 #  define _G_TYPE_CCC(cp, gt, ct) \
     ((ct*) (void *) g_type_check_class_cast ((GTypeClass*) cp, gt))
-#else /* G_DISABLE_CAST_CHECKS */
-#  define _G_TYPE_CIC(ip, gt, ct)       ((ct*) ip)
-#  define _G_TYPE_CCC(cp, gt, ct)       ((ct*) cp)
-#endif /* G_DISABLE_CAST_CHECKS */
+#endif
+
 #define _G_TYPE_CHI(ip)			(g_type_check_instance ((GTypeInstance*) ip))
 #define _G_TYPE_CHV(vl)			(g_type_check_value ((GValue*) vl))
 #define _G_TYPE_IGC(ip, gt, ct)         ((ct*) (((GTypeInstance*) ip)->g_class))