diff --git a/ndn-cpp/key.hpp b/ndn-cpp/key.hpp
index da9a11f..6bfd779 100644
--- a/ndn-cpp/key.hpp
+++ b/ndn-cpp/key.hpp
@@ -68,7 +68,7 @@
   setKeyData(const std::vector<uint8_t>& keyData) { keyData_ = keyData; }
   
   void 
-  setKeyData(const uint8_t *keyData, unsigned int keyDataLength) 
+  setKeyData(const uint8_t *keyData, size_t keyDataLength) 
   { 
     keyData_ = Blob(keyData, keyDataLength); 
   }