Index: generic/gentclAPI.tcl
===================================================================
diff -u -N -r827f6d934f60d5ea0c02ea68d9e4cb8fc8a2f7ad -rc96782fabd01fbfc8d11365dcc649d2788f78aa3
--- generic/gentclAPI.tcl	(.../gentclAPI.tcl)	(revision 827f6d934f60d5ea0c02ea68d9e4cb8fc8a2f7ad)
+++ generic/gentclAPI.tcl	(.../gentclAPI.tcl)	(revision c96782fabd01fbfc8d11365dcc649d2788f78aa3)
@@ -137,13 +137,15 @@
       set if [list "NsfClass *cl"]
       append intro \
           "  NsfClass *cl =  NsfObjectToClass(clientData);" \n \
+          "  assert(objc > 0);" \n \
           "  if (unlikely(cl == NULL)) return NsfDispatchClientDataError(interp, clientData, \"class\", ObjStr(objv\[0\]));"
     }
     object {
       set a  [list obj]
       set if [list "NsfObject *obj"]
       append intro \
           "  NsfObject *obj =  (NsfObject *)clientData;" \n \
+          "  assert(objc > 0);" \n \
           "  if (unlikely(obj == NULL)) return NsfDispatchClientDataError(interp, clientData, \"object\",  ObjStr(objv\[0\]));"
     }
     ""    {