diff --git a/lib/RedisData/RedisBlacklistStore.ts b/lib/RedisData/RedisBlacklistStore.ts
index 7274877..f91fafb 100644
--- a/lib/RedisData/RedisBlacklistStore.ts
+++ b/lib/RedisData/RedisBlacklistStore.ts
@@ -20,7 +20,7 @@ export class RedisBlacklistStore extends Redis {
     }
     await this.redis.setex (
       `blacklist_${key}`,
-      (valid_until.getTime () - Date.now ()) / 1000,
+      Math.floor ((valid_until.getTime () - Date.now ()) / 1000),
       1
     );
     log ('saved key');