diff --git a/ledis/const.go b/ledis/const.go
index 9e4d0cf..ba0cf05 100644
--- a/ledis/const.go
+++ b/ledis/const.go
@@ -37,4 +37,5 @@ var (
 	ErrKeySize        = errors.New("invalid key size")
 	ErrHashFieldSize  = errors.New("invalid hash field size")
 	ErrZSetMemberSize = errors.New("invalid zset member size")
+	ErrScoreMiss      = errors.New("zset score miss")
 )
diff --git a/ledis/t_zset.go b/ledis/t_zset.go
index 372368e..8be54b7 100644
--- a/ledis/t_zset.go
+++ b/ledis/t_zset.go
@@ -22,7 +22,6 @@ var errZSizeKey = errors.New("invalid zsize key")
 var errZSetKey = errors.New("invalid zset key")
 var errZScoreKey = errors.New("invalid zscore key")
 var errScoreOverflow = errors.New("zset score overflow")
-var errScoreMiss = errors.New("zset score miss")
 
 const (
 	zsetNScoreSep    byte = '<'
@@ -324,7 +323,7 @@ func (db *DB) ZScore(key []byte, member []byte) (int64, error) {
 	if v, err := db.db.Get(k); err != nil {
 		return InvalidScore, err
 	} else if v == nil {
-		return InvalidScore, errScoreMiss
+		return InvalidScore, ErrScoreMiss
 	} else {
 		if score, err = Int64(v, nil); err != nil {
 			return InvalidScore, err
diff --git a/server/cmd_zset.go b/server/cmd_zset.go
index c68f71b..d9cb78a 100644
--- a/server/cmd_zset.go
+++ b/server/cmd_zset.go
@@ -67,9 +67,13 @@ func zscoreCommand(c *client) error {
 	}
 
 	if s, err := c.db.ZScore(args[0], args[1]); err != nil {
-		return err
+		if err == ledis.ErrScoreMiss {
+			c.writeBulk(nil)
+		} else {
+			return err
+		}
 	} else {
-		c.writeInteger(s)
+		c.writeBulk(ledis.StrPutInt64(s))
 	}
 
 	return nil