diff --git a/ndn-cpp/security/identity/memory-identity-storage.hpp b/ndn-cpp/security/identity/memory-identity-storage.hpp
index dc8509d..980f78d 100644
--- a/ndn-cpp/security/identity/memory-identity-storage.hpp
+++ b/ndn-cpp/security/identity/memory-identity-storage.hpp
@@ -79,7 +79,7 @@
    * @param publicKeyDer A blob of the public key DER to be added.
    */
   virtual void 
-  addKey(const Name& keyName, KeyType keyType, Blob& publicKeyDer);
+  addKey(const Name& keyName, KeyType keyType, const Blob& publicKeyDer);
 
   /**
    * Get the public key DER blob from the identity storage.