diff --git a/README.md b/README.md
index 8fcc921..4095346 100644
--- a/README.md
+++ b/README.md
@@ -2,9 +2,12 @@ wetness
 =======
 
 `wetness` is a `bash` script for checking a CSS file for duplicate properties.
-
 Just like [Ellie Kemper][BJ], the aim of this script is to help make it DRY.
 
+This script utilizes associative arrays in `bash` which requires version 4. OSX
+is still shipping with version 3.2 but you can upgrade to 4.2 with
+`brew install bash`.
+
   [BJ]: http://www.collegehumor.com/video/1183463/derrick-comedy-blowjob
 
 ## Usage