diff --git a/README.md b/README.md
index 76a25b1..9c6cfc7 100644
--- a/README.md
+++ b/README.md
@@ -14,6 +14,7 @@ Requirements
 ============
 - bash (cygwin is OK)
 - wget
+- GNU grep (on MacOS install with `brew install grep --with-default-names`)
 
 Usage
 =====