diff --git a/ndn-cpp/c/util/crypto.h b/ndn-cpp/c/util/crypto.h
index eb7cec5..5bec549 100644
--- a/ndn-cpp/c/util/crypto.h
+++ b/ndn-cpp/c/util/crypto.h
@@ -21,7 +21,7 @@
  * @param dataLength The length of data.
  * @param digest A pointer to a buffer of size SHA256_DIGEST_LENGTH to receive the data.
  */
-void ndn_digestSha256(const uint8_t *data, unsigned int dataLength, uint8_t *digest);
+void ndn_digestSha256(const uint8_t *data, size_t dataLength, uint8_t *digest);
 
 #ifdef __cplusplus
 }