diff --git a/src/sentinel.c b/src/sentinel.c
index d097a604..fee3153f 100644
--- a/src/sentinel.c
+++ b/src/sentinel.c
@@ -2386,6 +2386,7 @@ void sentinelCommand(redisClient *c) {
         /* SENTINEL MASTER <name> */
         sentinelRedisInstance *ri;
 
+        if (c->argc != 3) goto numargserr;
         if ((ri = sentinelGetMasterByNameOrReplyError(c,c->argv[2]))
             == NULL) return;
         addReplySentinelRedisInstance(c,ri);