diff --git a/src/PubSubClient.h b/src/PubSubClient.h
index d2cc61c8..073a7590 100755
--- a/src/PubSubClient.h
+++ b/src/PubSubClient.h
@@ -66,7 +66,11 @@
 #define MQTTQOS1        (1 << 1)
 #define MQTTQOS2        (2 << 1)
 
+#ifdef ESP8266
 #define MQTT_CALLBACK_SIGNATURE std::function<void(char*, uint8_t*, uint32_t)> callback
+#else
+#define MQTT_CALLBACK_SIGNATURE void (*callback)(char*, uint8_t*, uint32_t)
+#endif
 
 class PubSubClient {
 private: