diff --git a/lib/mosquitto.c b/lib/mosquitto.c
index 4334854b..3dfe4f1d 100644
--- a/lib/mosquitto.c
+++ b/lib/mosquitto.c
@@ -139,6 +139,7 @@ int mosquitto_reinitialise(struct mosquitto *mosq, const char *id, bool clean_se
 	}else{
 		mosq->userdata = mosq;
 	}
+	mosq->protocol = mosq_p_mqtt31;
 	mosq->sock = INVALID_SOCKET;
 	mosq->sockpairR = INVALID_SOCKET;
 	mosq->sockpairW = INVALID_SOCKET;