Referencable is not a word, so don't use it in an error message <wink>.
diff --git a/Objects/weakrefobject.c b/Objects/weakrefobject.c
index e821154..e9d0b4b 100644
--- a/Objects/weakrefobject.c
+++ b/Objects/weakrefobject.c
@@ -558,7 +558,7 @@
 
     if (!PyType_SUPPORTS_WEAKREFS(ob->ob_type)) {
         PyErr_Format(PyExc_TypeError,
-                     "'%s' objects are not weakly referencable",
+		     "cannot create weak reference to '%s' object",
                      ob->ob_type->tp_name);
         return NULL;
     }
@@ -602,7 +602,7 @@
 
     if (!PyType_SUPPORTS_WEAKREFS(ob->ob_type)) {
         PyErr_Format(PyExc_TypeError,
-                     "'%s' objects are not weakly referencable",
+		     "cannot create weak reference to '%s' object",
                      ob->ob_type->tp_name);
         return NULL;
     }