diff --git a/lorawan.h b/lorawan.h
index c6da1e7e7584b582d8004543ecf341c8ba85a193..fe4c9e4912008a894bc3ba8bb0de8a0e124d506b 100644
--- a/lorawan.h
+++ b/lorawan.h
@@ -40,7 +40,7 @@ namespace lorawan {
   extern String last_transmission;
   void initialize();
   void process();
-  void preparePayloadIfTimeHasCome(int16_t co2, float temp, float hum);
+  void preparePayloadIfTimeHasCome(const int16_t &co2, const float &temp, const float &hum);
 }
 
 #endif
diff --git a/mqtt.cpp b/mqtt.cpp
index 826ced5a6c7fd03c1466ba9762d131d9eb64ad1e..e7e6e33f12bb6f21cbccbb1fa52566ef5b4d1782 100644
--- a/mqtt.cpp
+++ b/mqtt.cpp
@@ -207,7 +207,7 @@ namespace mqtt {
     }
   }
 
-  void publishIfTimeHasCome(const String &timeStamp, int16_t co2, float temp, float hum) {
+  void publishIfTimeHasCome(const String &timeStamp, const int16_t &co2, const float &temp, const float &hum) {
     // Send message via MQTT according to sending interval
     unsigned long now = seconds();
     //TODO: Send average since last MQTT message?
diff --git a/mqtt.h b/mqtt.h
index 6e43644336620607188b34b1bccfe650141eb546..9af46c8e60eb19650635244a7cd8ab09545b9cc1 100644
--- a/mqtt.h
+++ b/mqtt.h
@@ -9,12 +9,12 @@
 #include "src/lib/PubSubClient/src/PubSubClient.h"
 #include "wifi_util.h"
 namespace config {
-  extern uint16_t sending_interval;  // [s]
+  extern uint16_t sending_interval; // [s]
 }
 namespace mqtt {
   extern String last_successful_publish;
   void initialize(String &topic);
   void keepConnection();
-  void publishIfTimeHasCome(const String &timeStamp, int16_t co2, float temp, float hum);
+  void publishIfTimeHasCome(const String &timeStamp, const int16_t &co2, const float &temp, const float &hum);
 }
 #endif