diff --git a/src/source/downloading.md b/src/source/downloading.md
index 42008e5..93f49aa 100644
--- a/src/source/downloading.md
+++ b/src/source/downloading.md
@@ -39,6 +39,7 @@
 After installing Repo, set up your client to access the android source repository:
 
  - Create an empty directory to hold your working files.
+ If you're using MacOS, this has to be on a case-sensitive filesystem.
  Give it any name you like: