diff --git a/staging/src/k8s.io/client-go/tools/cache/controller.go b/staging/src/k8s.io/client-go/tools/cache/controller.go
index 73e7f8d7ae6..27a1c52cdfc 100644
--- a/staging/src/k8s.io/client-go/tools/cache/controller.go
+++ b/staging/src/k8s.io/client-go/tools/cache/controller.go
@@ -131,6 +131,8 @@ func (c *controller) HasSynced() bool {
 }
 
 func (c *controller) LastSyncResourceVersion() string {
+	c.reflectorMutex.RLock()
+	defer c.reflectorMutex.RUnlock()
 	if c.reflector == nil {
 		return ""
 	}