diff --git a/js/src/vm/Shape.cpp b/js/src/vm/Shape.cpp
index a64dc529a6..306a2c5400 100644
--- a/js/src/vm/Shape.cpp
+++ b/js/src/vm/Shape.cpp
@@ -1214,6 +1214,10 @@ JSObject::setFlags(ExclusiveContext* cx, BaseShape::Flag flags, GenerateShape ge
 
     RootedObject self(cx, this);
 
+    Shape* existingShape = self->ensureShape(cx);
+    if (!existingShape)
+        return false;
+
     if (isNative() && as<NativeObject>().inDictionaryMode()) {
         if (generateShape == GENERATE_SHAPE && !as<NativeObject>().generateOwnShape(cx))
             return false;
@@ -1227,10 +1231,6 @@ JSObject::setFlags(ExclusiveContext* cx, BaseShape::Flag flags, GenerateShape ge
         return true;
     }
 
-    Shape* existingShape = self->ensureShape(cx);
-    if (!existingShape)
-        return false;
-
     Shape* newShape = Shape::setObjectFlags(cx, flags, self->taggedProto(), existingShape);
     if (!newShape)
         return false;