diff --git a/README.rst b/README.rst
index 21bd63fd6..5ffcff22c 100644
--- a/README.rst
+++ b/README.rst
@@ -120,6 +120,7 @@ Installing prerequisites on Mac OS X::
     xcode-select --install
     sudo easy_install pip
     sudo pip install virtualenv
+    brew install pkg-config libffi
 
 Installing prerequisites on Raspbian::