diff --git a/model/pit/ndn-pit-entry-incoming-face.h b/model/pit/ndn-pit-entry-incoming-face.h
index 8ff7947..cd75643 100644
--- a/model/pit/ndn-pit-entry-incoming-face.h
+++ b/model/pit/ndn-pit-entry-incoming-face.h
@@ -55,7 +55,7 @@
    * @brie Copy operator
    */
   IncomingFace &
-  operator = (IncomingFace &other);
+  operator = (const IncomingFace &other);
 
   /**
    * @brief Compare two PitEntryIncomingFace