diff --git a/lib/js/runtime.sx b/lib/js/runtime.sx
index 080f937a..b8bbf7b8 100644
--- a/lib/js/runtime.sx
+++ b/lib/js/runtime.sx
@@ -739,12 +739,18 @@
   js-get-ctor-proto
   (fn
     (ctor)
-    (let
-      ((id (js-ctor-id ctor)))
-      (cond
-        ((dict-has? __js_proto_table__ id) (get __js_proto_table__ id))
-        (else
-          (let ((p (dict))) (begin (dict-set! __js_proto_table__ id p) p)))))))
+    (cond
+      ((and (= (type-of ctor) "dict") (contains? (keys ctor) "prototype"))
+        (get ctor "prototype"))
+      (else
+        (let
+          ((id (js-ctor-id ctor)))
+          (cond
+            ((dict-has? __js_proto_table__ id) (get __js_proto_table__ id))
+            (else
+              (let
+                ((p (dict)))
+                (begin (dict-set! __js_proto_table__ id p) p)))))))))
 (define
   js-reset-ctor-proto!
   (fn