diff --git a/doc/esp8266wifi/generic-class.rst b/doc/esp8266wifi/generic-class.rst
index bf6228d4e..58e1fba3c 100644
--- a/doc/esp8266wifi/generic-class.rst
+++ b/doc/esp8266wifi/generic-class.rst
@@ -61,6 +61,8 @@ linker).
 
 .. code:: cpp
 
+    #include <ESP8266WiFi.h>    // necessary to avoid a linker error
+
     void setup () {
     #ifdef WIFI_IS_OFF_AT_BOOT
         enableWiFiAtBootTime(); // can be called from anywhere with the same effect