diff --git a/tsdb/meta.go b/tsdb/meta.go
index feb10f8ffb..29ee56aa34 100644
--- a/tsdb/meta.go
+++ b/tsdb/meta.go
@@ -158,9 +158,7 @@ func (d *DatabaseIndex) CreateMeasurementIndexIfNotExists(name string) *Measurem
 func (d *DatabaseIndex) AssignShard(k string, shardID uint64) {
 	ss := d.Series(k)
 	if ss != nil {
-		d.mu.Lock()
 		ss.AssignShard(shardID)
-		d.mu.Unlock()
 	}
 }
 
@@ -168,6 +166,7 @@ func (d *DatabaseIndex) AssignShard(k string, shardID uint64) {
 func (d *DatabaseIndex) TagsForSeries(key string) map[string]string {
 	d.mu.RLock()
 	defer d.mu.RUnlock()
+
 	ss := d.series[key]
 	if ss == nil {
 		return nil
@@ -1311,9 +1310,9 @@ func (a Measurements) union(other Measurements) Measurements {
 
 // Series belong to a Measurement and represent unique time series in a database
 type Series struct {
-	Key  string
-	Tags map[string]string
-
+	mu          sync.RWMutex
+	Key         string
+	Tags        map[string]string
 	id          uint64
 	measurement *Measurement
 	shardIDs    map[uint64]bool // shards that have this series defined
@@ -1329,11 +1328,16 @@ func NewSeries(key string, tags map[string]string) *Series {
 }
 
 func (s *Series) AssignShard(shardID uint64) {
+	s.mu.Lock()
 	s.shardIDs[shardID] = true
+	s.mu.Unlock()
 }
 
 // MarshalBinary encodes the object to a binary format.
 func (s *Series) MarshalBinary() ([]byte, error) {
+	s.mu.RLock()
+	defer s.mu.RUnlock()
+
 	var pb internal.Series
 	pb.Key = &s.Key
 	for k, v := range s.Tags {
@@ -1346,6 +1350,9 @@ func (s *Series) MarshalBinary() ([]byte, error) {
 
 // UnmarshalBinary decodes the object from a binary format.
 func (s *Series) UnmarshalBinary(buf []byte) error {
+	s.mu.Lock()
+	defer s.mu.Unlock()
+
 	var pb internal.Series
 	if err := proto.Unmarshal(buf, &pb); err != nil {
 		return err
@@ -1360,11 +1367,16 @@ func (s *Series) UnmarshalBinary(buf []byte) error {
 
 // InitializeShards initializes the list of shards.
 func (s *Series) InitializeShards() {
+	s.mu.Lock()
 	s.shardIDs = make(map[uint64]bool)
+	s.mu.Unlock()
 }
 
 // match returns true if all tags match the series' tags.
 func (s *Series) match(tags map[string]string) bool {
+	s.mu.RLock()
+	defer s.mu.RUnlock()
+
 	for k, v := range tags {
 		if s.Tags[k] != v {
 			return false