diff --git a/proxy/grpcproxy/watch.go b/proxy/grpcproxy/watch.go
index 639bf8e2d..8dee6e343 100644
--- a/proxy/grpcproxy/watch.go
+++ b/proxy/grpcproxy/watch.go
@@ -240,6 +240,7 @@ func (wps *watchProxyStream) recvLoop() error {
 				continue
 			}
 
+			wps.mu.Lock()
 			w := &watcher{
 				wr:  watchRange{string(cr.Key), string(cr.RangeEnd)},
 				id:  wps.nextWatcherID,
@@ -258,6 +259,7 @@ func (wps *watchProxyStream) recvLoop() error {
 			w.nextrev = cr.StartRevision
 			wps.watchers[w.id] = w
 			wps.ranges.add(w)
+			wps.mu.Unlock()
 		case *pb.WatchRequest_CancelRequest:
 			wps.delete(uv.CancelRequest.WatchId)
 		default: