diff --git a/CONTRIBUTING.md b/CONTRIBUTING.md
index 13e2ad7..bc4b288 100644
--- a/CONTRIBUTING.md
+++ b/CONTRIBUTING.md
@@ -11,6 +11,7 @@ Fortunately, there's not many dependencies:
 - OpenJDK 8
 - Android SDK: build tools (minimum `28.0.1`), platform `30`
 - Make sure to have the `$ANDROID_HOME` environment variable set.
+- FontForge version >= 20201107
 
 For Nix users, there's a `shell.nix` for setting-up the right environment.
 
@@ -23,6 +24,9 @@ make
 If the build succeed, the debug apk is located in
 `_build/juloo.keyboard2.debug.apk`.
 
+If the build doesn't succeeded check the FontForge version, the version needed is 20201107. 
+Try to use the nix-shell, instructions to install [here](https://nixos.wiki/wiki/Nix_Installation_Guide)
+
 ## Using the local debug.keystore on the Github CI actions
 
 It's possible to save the local debug.keystore into a github secret, so the same keystore is utilized to build the debug apk in the CI github actions.