diff --git a/src/libsodium/crypto_pwhash/scryptsalsa208sha256/pbkdf2-sha256.c b/src/libsodium/crypto_pwhash/scryptsalsa208sha256/pbkdf2-sha256.c
index d4faf69f..ff6ba577 100644
--- a/src/libsodium/crypto_pwhash/scryptsalsa208sha256/pbkdf2-sha256.c
+++ b/src/libsodium/crypto_pwhash/scryptsalsa208sha256/pbkdf2-sha256.c
@@ -53,7 +53,7 @@ PBKDF2_SHA256(const uint8_t * passwd, size_t passwdlen, const uint8_t * salt,
     int             k;
     size_t          clen;
 
-    if (dkLen > 0x1fffffffe0UL) {
+    if (dkLen > 0x1fffffffe0ULL) {
         abort();
     }
     crypto_auth_hmacsha256_init(&PShctx, passwd, passwdlen);