diff --git a/tools/aapt2/ResourceUtils.h b/tools/aapt2/ResourceUtils.h
index 31b8e89..a57d89d 100644
--- a/tools/aapt2/ResourceUtils.h
+++ b/tools/aapt2/ResourceUtils.h
@@ -163,11 +163,11 @@
  */
 std::unique_ptr<Item> parseItemForAttribute(
         const StringPiece& value, const Attribute* attr,
-        std::function<void(const ResourceName&)> onCreateReference = {});
+        const std::function<void(const ResourceName&)>& onCreateReference = {});
 
 std::unique_ptr<Item> parseItemForAttribute(
         const StringPiece& value, uint32_t typeMask,
-        std::function<void(const ResourceName&)> onCreateReference = {});
+        const std::function<void(const ResourceName&)>& onCreateReference = {});
 
 uint32_t androidTypeToAttributeTypeMask(uint16_t type);