diff --git a/batchconsumer/batcher/message_batcher.go b/batchconsumer/batcher/message_batcher.go
index 6aa9a64..4ac1d54 100644
--- a/batchconsumer/batcher/message_batcher.go
+++ b/batchconsumer/batcher/message_batcher.go
@@ -133,8 +133,10 @@ func (b *batcher) batchSize(batch [][]byte) int {
 
 func (b *batcher) flush(batch [][]byte) [][]byte {
 	if len(batch) > 0 {
+		b.mux.Lock()
 		b.sync.SendBatch(batch)
 		b.smallestSeq = SequencePair{nil, 0}
+		b.mux.Unlock()
 	}
 	return [][]byte{}
 }