diff --git a/js/src/jsinterp.cpp b/js/src/jsinterp.cpp
index af08c43916e..c38d0a3f958 100644
--- a/js/src/jsinterp.cpp
+++ b/js/src/jsinterp.cpp
@@ -5391,7 +5391,7 @@ BEGIN_CASE(JSOP_DEFFUN)
              * setter to an existing property without a getter or setter.
              */
             JS_ASSERT(!(attrs & ~(JSPROP_ENUMERATE|JSPROP_PERMANENT)));
-            JS_ASSERT(!(old & JSPROP_READONLY));
+            JS_ASSERT_IF(attrs != JSPROP_ENUMERATE, !(old & JSPROP_READONLY));
             doSet = true;
         }
         pobj->dropProperty(cx, prop);
diff --git a/js/src/methodjit/StubCalls.cpp b/js/src/methodjit/StubCalls.cpp
index 0f4e399b7fd..508c2f35dc5 100644
--- a/js/src/methodjit/StubCalls.cpp
+++ b/js/src/methodjit/StubCalls.cpp
@@ -954,7 +954,7 @@ stubs::DefFun(VMFrame &f, JSFunction *fun)
              * setter to an existing property without a getter or setter.
              */
             JS_ASSERT(!(attrs & ~(JSPROP_ENUMERATE|JSPROP_PERMANENT)));
-            JS_ASSERT(!(old & JSPROP_READONLY));
+            JS_ASSERT_IF(attrs != JSPROP_ENUMERATE, !(old & JSPROP_READONLY));
             doSet = true;
         }
         pobj->dropProperty(cx, prop);