I am new to the Arduino world and it seems that this simple problem is keeping me at the start line.

  • I use the Generic ESP8266 Module as Board
  • In my sketch I just write:
#include < ESP8266WiFi.h >
void setup(){}
void loop(){}

The ERROR is :

BearSSLHelpers.h:148:34: error: 'virtual const unsigned char* BearSSL::HashSHA256::oid()' marked override, but does not override

 virtual const unsigned char *oid() override;


How am I going to solve that? Any help is appreciated.

  • with esp8266 Arduino core 2.5.2 I can compile it without errors
    – Juraj
    Sep 19, 2019 at 17:32
  • Well, I can't.. Sep 19, 2019 at 17:35
  • Installed the ESP8266 Arduino core 2.5.2 and tried to run this simple code above Sep 19, 2019 at 17:41
  • 1) File > Preferences and on Additional Boards Manager URLs i pasted arduino.esp8266.com/stable/package_esp8266com_index.json 2) Tools > Board > Board Manager > typed "ESP8266" and installed ESP8266 by ESP8266 Community version 2.5.2 Sep 19, 2019 at 17:56
  • there is virtual const void *hash() override on line 148 in release
    – Juraj
    Sep 19, 2019 at 18:02

1 Answer 1


You installed the latest git version of the ESP8266WiFi library into your libraries folder and this version is not compatible with the 2.5.2 version of the esp82666 Arduino core.

The ESP8266WiFi library is part of the esp8266 boards package. It should not be installed separately. Delete the library from your libraries folder.

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