diff --git a/server/consumer.go b/server/consumer.go
index 8a046819d5..28951dec53 100644
--- a/server/consumer.go
+++ b/server/consumer.go
@@ -5787,12 +5787,14 @@ func (o *consumer) cleanupNoInterestMessages(mset *stream, ignoreInterest bool)
 		return
 	}
 
+	mset.mu.RUnlock()
+	mset.mu.Lock()
 	for seq := start; seq <= stop; seq++ {
 		if mset.noInterest(seq, co) {
 			rmseqs = append(rmseqs, seq)
 		}
 	}
-	mset.mu.RUnlock()
+	mset.mu.Unlock()
 
 	// These can be removed.
 	for _, seq := range rmseqs {