diff --git a/src/hash_impl.h b/src/hash_impl.h
index 956e0ea48b..1065acd643 100644
--- a/src/hash_impl.h
+++ b/src/hash_impl.h
@@ -265,7 +265,7 @@ static void secp256k1_rfc6979_hmac_sha256_generate(secp256k1_rfc6979_hmac_sha256
 
     while (outlen > 0) {
         secp256k1_hmac_sha256 hmac;
-        int now = outlen;
+        size_t now = outlen;
         secp256k1_hmac_sha256_initialize(&hmac, rng->k, 32);
         secp256k1_hmac_sha256_write(&hmac, rng->v, 32);
         secp256k1_hmac_sha256_finalize(&hmac, rng->v);