diff --git a/ndn-cpp/security/identity/memory-identity-storage.cpp b/ndn-cpp/security/identity/memory-identity-storage.cpp
index 1e4f0fc..587d231 100644
--- a/ndn-cpp/security/identity/memory-identity-storage.cpp
+++ b/ndn-cpp/security/identity/memory-identity-storage.cpp
@@ -73,7 +73,7 @@
 }
 
 void 
-MemoryIdentityStorage::addKey(const Name& keyName, KeyType keyType, Blob& publicKeyDer)
+MemoryIdentityStorage::addKey(const Name& keyName, KeyType keyType, const Blob& publicKeyDer)
 {
 #if 1
   throw std::runtime_error("MemoryIdentityStorage::addKey not implemented");