diff --git a/beacon-chain/sync/service.go b/beacon-chain/sync/service.go
index a56d7cfc29..1ded3d27dc 100644
--- a/beacon-chain/sync/service.go
+++ b/beacon-chain/sync/service.go
@@ -66,6 +66,7 @@ type RegularSync struct {
 	pendingQueueLock    sync.RWMutex
 	chainStarted        bool
 	initialSync         Checker
+	validateBlockLock    sync.RWMutex
 }
 
 // Start the regular sync service.
diff --git a/beacon-chain/sync/validate_beacon_blocks.go b/beacon-chain/sync/validate_beacon_blocks.go
index 5c86593f81..242bb5b8ce 100644
--- a/beacon-chain/sync/validate_beacon_blocks.go
+++ b/beacon-chain/sync/validate_beacon_blocks.go
@@ -19,6 +19,8 @@ var recentlySeenRoots = ccache.New(ccache.Configure().MaxSize(100000))
 // Blocks that have already been seen are ignored. If the BLS signature is any valid signature,
 // this method rebroadcasts the message.
 func (r *RegularSync) validateBeaconBlockPubSub(ctx context.Context, msg proto.Message, p p2p.Broadcaster, fromSelf bool) bool {
+	r.validateBlockLock.Lock()
+	defer r.validateBlockLock.Unlock()
 	m := msg.(*ethpb.BeaconBlock)
 
 	blockRoot, err := ssz.SigningRoot(m)