diff --git a/docs/en/index.md b/docs/en/index.md
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+++ b/docs/en/index.md
@@ -2,7 +2,7 @@
 
 NodeMCU is an [eLua](http://www.eluaproject.net/) based firmware for the [ESP8266 WiFi SOC from Espressif](http://espressif.com/en/products/esp8266/). This is a companion project to the popular [NodeMCU dev kits](https://github.com/nodemcu/nodemcu-devkit-v1.0), ready-made open source development boards with ESP8266-12E chips.
 
-The firmware is based on the Espressif SDK v1.4 and uses a file system based on [spiffs](https://github.com/pellepl/spiffs).
+The firmware is based on the Espressif NON-OS SDK and uses a file system based on [spiffs](https://github.com/pellepl/spiffs).
 
 ## Getting started
 - [Build the firmeware](build.md) with the modules you need.