diff --git a/doc/source/dev/tests.rst b/doc/source/dev/tests.rst
index 77f9d2dd7..8d552c875 100644
--- a/doc/source/dev/tests.rst
+++ b/doc/source/dev/tests.rst
@@ -5,6 +5,6 @@ You need to have `tox` and `bundler` installed for running the tests.
 
 Quickstart for Ubuntu Trusty::
 
-    apt-get install tox ruby
+    apt-get install tox ruby ruby1.9.1-dev
     gem install bundler
     tox