diff --git a/js/src/jsarray.cpp b/js/src/jsarray.cpp
index a99c0f1f5bb0..0cad8d019470 100644
--- a/js/src/jsarray.cpp
+++ b/js/src/jsarray.cpp
@@ -573,8 +573,7 @@ js::ArraySetLength(JSContext* cx, Handle<ArrayObject*> arr, HandleId id,
     {
         RootedShape lengthShape(cx, arr->lookupPure(id));
         MOZ_ASSERT(lengthShape);
-        MOZ_ASSERT_IF(lengthIsWritable, lengthShape->writable());
-        MOZ_ASSERT_IF(lengthShape->writable() && !lengthIsWritable, arr->denseElementsAreFrozen());
+        MOZ_ASSERT(lengthShape->writable() == lengthIsWritable);
     }
 #endif
     uint32_t oldLen = arr->length();
diff --git a/js/src/vm/NativeObject.h b/js/src/vm/NativeObject.h
index f1f7d0e8ea5c..3eb816bd850b 100644
--- a/js/src/vm/NativeObject.h
+++ b/js/src/vm/NativeObject.h
@@ -228,8 +228,7 @@ class ObjectElements
         flags &= ~CONVERT_DOUBLE_ELEMENTS;
     }
     bool hasNonwritableArrayLength() const {
-        return flags & NONWRITABLE_ARRAY_LENGTH ||
-               flags & FROZEN;
+        return flags & NONWRITABLE_ARRAY_LENGTH;
     }
     void setNonwritableArrayLength() {
         MOZ_ASSERT(!isCopyOnWrite());