diff --git a/ndn-cpp/security/identity/identity-storage.hpp b/ndn-cpp/security/identity/identity-storage.hpp
index daead73..0e22432 100644
--- a/ndn-cpp/security/identity/identity-storage.hpp
+++ b/ndn-cpp/security/identity/identity-storage.hpp
@@ -83,7 +83,7 @@
    * @param publicKeyDer A blob of the public key DER to be added.
    */
   virtual void 
-  addKey(const Name& keyName, KeyType keyType, Blob& publicKeyDer) = 0;
+  addKey(const Name& keyName, KeyType keyType, const Blob& publicKeyDer) = 0;
 
   /**
    * Get the public key DER blob from the identity storage.