diff --git a/grpc_client_test.go b/grpc_client_test.go
index a2db4b3..30e719e 100644
--- a/grpc_client_test.go
+++ b/grpc_client_test.go
@@ -37,6 +37,9 @@ import (
 )
 
 func (c *GrpcClients) getWakeupChannelForTesting() <-chan struct{} {
+	c.mu.Lock()
+	defer c.mu.Unlock()
+
 	if c.wakeupChanForTesting != nil {
 		return c.wakeupChanForTesting
 	}