disambiguate a version number
diff --git a/docs/installation.rst b/docs/installation.rst
index 6c25053..c948d40 100644
--- a/docs/installation.rst
+++ b/docs/installation.rst
@@ -182,8 +182,8 @@
If you want to build cryptography yourself or are on an older OS X version
cryptography requires the presence of a C compiler, development headers, and
the proper libraries. On OS X much of this is provided by Apple's Xcode
-development tools. To install the Xcode command line tools (on 10.9+) open a
-terminal window and run:
+development tools. To install the Xcode command line tools (on OS X 10.9+)
+open a terminal window and run:
.. code-block:: console