defining a generic on something that is not a class would ruin the generic

library/generic/generic.factor

@@ -74,6 +74,9 @@ math-internals ;
 
 : define-method ( class generic definition -- )
     -rot
+    over metaclass word? [
+        word-name " is not a class" append throw
+    ] unless
     [ "methods" word-prop set-hash ] keep dup <vtable>
     make-generic ;
 

library/test/generic.factor

@@ -156,4 +156,4 @@ M: number union-containment drop 2 ;
 ! Testing recovery from bad method definitions
 "GENERIC: unhappy" eval
 [ "M: vocabularies unhappy ;" eval ] unit-test-fails
-[ ] [ "GENERIC: unhapy" eval ] unit-test
+[ ] [ "GENERIC: unhappy" eval ] unit-test