message: Update installation.rst for Ubuntu 16.04 LTS
  Ubuntu 16.04 by default install python2.7 alongside with python 3.5 and set python2.7 as default. If you have created a virtualenv with python3.5 compilation fails due to wrong python-dev library installed.
  If you install ``python3.5-dev`` the build for the wheel package of  ``cryptography`` run fine.
diff: @@ -53,6 +53,12 @@ the required dependencies are installed: ::
  sudo apt-get install build-essential libssl-dev libffi-dev python-dev python-pip libsasl2-dev libldap2-dev
  +**Ubuntu 16.04** If you have python3.5 installed alongside with python2.7, as is default on **Ubuntu 16.04 LTS**, run this command also
  +
  + sudo apt-get install build-essential libssl-dev libffi-dev python3.5-dev python-pip libsasl2-dev libldap2-dev
  +
  +otherwhise build for ``cryptography`` fails.
  +
  For **Fedora** and **RHEL-derivatives**, the following command will ensure
  that the required dependencies are installed: ::
  