diff --git a/CONTRIBUTING.md b/CONTRIBUTING.md
index 96d083ce..ab46e879 100644
--- a/CONTRIBUTING.md
+++ b/CONTRIBUTING.md
@@ -5,6 +5,7 @@ Contributions and pull requests are welcome.  Please take note of the following
 *  Adhere to the existing style as much as possible; notably, 2 space indents and long-form keywords.
 *  Keep the history clean!  Squash your branches before you submit a pull request.  `pull --rebase` is your friend.
 *  Any changes to the core should be tested against Vim 7.4.
+*  Contributers should install [thinca/vim-themis](https://github.com/thinca/vim-themis) to run tests before sending a PR if they applied some modification to the code. PRs which does not pass tests won't be accepted.
 
 # Bugs