diff --git a/core/classes/singleton/singleton-tests.factor b/core/classes/singleton/singleton-tests.factor
index 11a2a2d166..92a9877477 100644
--- a/core/classes/singleton/singleton-tests.factor
+++ b/core/classes/singleton/singleton-tests.factor
@@ -4,7 +4,7 @@ IN: classes.singleton.tests
 [ ] [ SINGLETON: bzzt ] unit-test
 [ t ] [ bzzt bzzt? ] unit-test
 [ t ] [ bzzt bzzt eq? ] unit-test
-GENERIC: zammo ( obj -- )
+GENERIC: zammo ( obj -- str )
 [ ] [ M: bzzt zammo drop "yes!" ; ] unit-test
 [ "yes!" ] [ bzzt zammo ] unit-test
 [ ] [ SINGLETON: omg ] unit-test