diff --git a/src/EspalexaDevice.h b/src/EspalexaDevice.h
index 4785591..0653a41 100644
--- a/src/EspalexaDevice.h
+++ b/src/EspalexaDevice.h
@@ -2,6 +2,7 @@
 #define EspalexaDevice_h
 
 #include "Arduino.h"
+#include <functional>
 
 typedef class EspalexaDevice;