--- JSON-XS/typemap	2007/07/02 07:39:31	1.1
+++ JSON-XS/typemap	2007/11/28 13:57:15	1.3
@@ -3,8 +3,13 @@
 INPUT
 
 T_JSON
-	if (!(SvROK ($arg) && SvOBJECT (SvRV ($arg)) && SvSTASH (SvRV ($arg)) == json_stash))
+	if (!(
+           SvROK ($arg)
+           && SvOBJECT (SvRV ($arg))
+           && (SvSTASH (SvRV ($arg)) == JSON_STASH || sv_derived_from ($arg, \"JSON::XS\"))
+        ))
           croak (\"object is not of type JSON::XS\");
+        /**/
         $var = (JSON *)SvPVX (SvRV ($arg));