diff --git a/ndn-cpp/c/util/crypto.c b/ndn-cpp/c/util/crypto.c
index 2cdc91b..ec13f68 100644
--- a/ndn-cpp/c/util/crypto.c
+++ b/ndn-cpp/c/util/crypto.c
@@ -6,7 +6,7 @@
 
 #include "crypto.h"
 
-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)
 {
   SHA256_CTX sha256;
   SHA256_Init(&sha256);