diff --git a/etc/inc/voucher.inc b/etc/inc/voucher.inc
index 00cb397b30..863cc171e5 100644
--- a/etc/inc/voucher.inc
+++ b/etc/inc/voucher.inc
@@ -557,6 +557,9 @@ function voucher_configure_zone($sync = false) {
             foreach ($config['voucher'][$cpzone]['roll'] as $rollent) {
 
                 $roll = $rollent['number'];
+		$len = ($rollent['count'] >> 3) + 1;
+		if (strlen(base64_decode($rollent['used'])) != $len)
+			$rollent['used'] = base64_encode(str_repeat("\000", $len));
                 voucher_write_used_db($roll, $rollent['used']);
                 $minutes = $rollent['minutes'];
                 $active_vouchers = array();