diff --git a/libnetwork/networkdb/cluster.go b/libnetwork/networkdb/cluster.go
index 37bb3536f4..fc6ac698d8 100644
--- a/libnetwork/networkdb/cluster.go
+++ b/libnetwork/networkdb/cluster.go
@@ -112,14 +112,20 @@ func (nDB *NetworkDB) clusterInit() error {
 
 	nDB.networkBroadcasts = &memberlist.TransmitLimitedQueue{
 		NumNodes: func() int {
-			return len(nDB.nodes)
+			nDB.RLock()
+			num := len(nDB.nodes)
+			nDB.RUnlock()
+			return num
 		},
 		RetransmitMult: config.RetransmitMult,
 	}
 
 	nDB.nodeBroadcasts = &memberlist.TransmitLimitedQueue{
 		NumNodes: func() int {
-			return len(nDB.nodes)
+			nDB.RLock()
+			num := len(nDB.nodes)
+			nDB.RUnlock()
+			return num
 		},
 		RetransmitMult: config.RetransmitMult,
 	}