diff --git a/.github/CONTRIBUTING.md b/.github/CONTRIBUTING.md
index 04a7cc1c..955af1ef 100644
--- a/.github/CONTRIBUTING.md
+++ b/.github/CONTRIBUTING.md
@@ -36,7 +36,7 @@ There are currently two files which need to be edited:
    make re2c
    ```
 
-   To run [`re2c`](http://re2c.org) and generate/overwrite file `src/json.hpp` with your changes in file `src/json.hpp.re2c`.
+   To run [`re2c`](http://re2c.org) and generate/overwrite file `src/json.hpp` with your changes in file `src/json.hpp.re2c`. We currently use re2c version 0.16. Please also use this version, because other re2c versions tend to create code that differs a lot from which makes diffs unusable.
 
 
 2. [`test/src/unit.cpp`](https://github.com/nlohmann/json/blob/master/test/unit.cpp) - This contains the [Catch](https://github.com/philsquared/Catch) unit tests which currently cover [100 %](https://coveralls.io/github/nlohmann/json) of the library's code.