diff --git a/docs/mac_build_instructions.md b/docs/mac_build_instructions.md
index 45659c6c37eb9..57571c3cb3770 100644
--- a/docs/mac_build_instructions.md
+++ b/docs/mac_build_instructions.md
@@ -357,3 +357,13 @@ Only accepting for all users of the machine requires root:
 ```shell
 $ sudo xcodebuild -license
 ```
+
+### Exclude checkout from Spotlight indexing
+
+Chromium's checkout contains a lot of files, and building generates many more.
+Spotlight will try to index all of those files, and uses a lot of CPU time
+doing so, especially during a build, which can slow things down.
+
+To prevent the Chromium checkout from being indexed by Spotlight, open System
+Preferences, go to "Spotlight" -> "Privacy" and add your Chromium checkout
+directory to the list of excluded locations.