diff --git a/OpenMQTTGateway.ino b/OpenMQTTGateway.ino
index f7a7e74..7a70488 100644
--- a/OpenMQTTGateway.ino
+++ b/OpenMQTTGateway.ino
@@ -750,7 +750,7 @@ void storeValue(unsigned long MQTTvalue){
     ReceivedSignal[o][0] = MQTTvalue;
     ReceivedSignal[o][1] = now;
     trc(F("store code :"));
-    trc(ReceivedSignal[o][0]+"/"+ReceivedSignal[o][1]);
+    trc(String(ReceivedSignal[o][0])+"/"+String(ReceivedSignal[o][1]));
     trc(F("Col: val/timestamp"));
     for (int i = 0; i < array_size; i++)
     {