diff --git a/Running-from-source.md b/Running-from-source.md
index d681f2e..b416782 100644
--- a/Running-from-source.md
+++ b/Running-from-source.md
@@ -4,6 +4,11 @@ Running from source
 You will currently need at least Python 3.7.x to run `stable` code.  In order to run
 `develop` you will need Python 3.8.x or higher (3.9.x has had some testing).
 
+1. On MacOS you will likely need a Python install from [the official Python 
+   website](https://www.python.org/), rather than using HomeBrew.  See
+   [#670 Update requirements.txt for MacOS](https://github.com/EDCD/EDMarketConnector/issues/670)
+   for discussion about this.
+
 1. You have two choices:
     1. Using a zip of the latest stable source. Download and extract the
      [latest stable source code](https://github.com/EDCD/EDMarketConnector/archive/stable.zip).