diff --git a/ykval-verify.php b/ykval-verify.php
index c4b7216..6ac1c99 100644
--- a/ykval-verify.php
+++ b/ykval-verify.php
@@ -100,7 +100,7 @@ $myLog->log(LOG_DEBUG, "found protocol version $protocol_version");
  */
 $h = getHttpVal('h', '');
 $client = getHttpVal('id', '0');
-$timestamp = getHttpVal('timestamp', 0);
+$timestamp = getHttpVal('timestamp', '0');
 $otp = getHttpVal('otp', '');
 
 $otp = strtolower($otp);