diff --git a/src/MQTTClient.h b/src/MQTTClient.h
index f2cb3ca..e9d18c2 100644
--- a/src/MQTTClient.h
+++ b/src/MQTTClient.h
@@ -57,7 +57,7 @@ class MQTTClient {
   lwmqtt_err_t _lastError = (lwmqtt_err_t)0;
 
  public:
-  void * ref;
+  void * ref = nullptr;
 
   explicit MQTTClient(int bufSize = 128);