diff --git a/README.md b/README.md
index eb83724..2bba52d 100644
--- a/README.md
+++ b/README.md
@@ -57,6 +57,9 @@ Feel free to reuse parts or the whole code if you want.
 * 1x 7cmx5cm pcb
 
 ## The software :
+**This code was tested against version 3.0.2 of the ESP8266 core SDK.**
+Use this version if it does not compile.
+
 ### Default FLASH Options (for the Arduino IDE) :
 ![](http://82.64.196.164/images/git/flash_option.png)