diff --git a/src/mzscheme/utils/xcglue.c b/src/mzscheme/utils/xcglue.c
index b7c74646d5..1acd8c9884 100644
--- a/src/mzscheme/utils/xcglue.c
+++ b/src/mzscheme/utils/xcglue.c
@@ -467,7 +467,7 @@ Scheme_Object *objscheme_unwrap(Scheme_Object *obj, Scheme_Object *c)
   Scheme_Object *s[1], *unwrapper, *unwrap_prop;
   Scheme_Class *cls = (Scheme_Class *)cls;
 
-  if (!obj)
+  if (!obj || !cls)
     return NULL;
 
   unwrap_prop = cls->unwrap_property;