diff --git a/CONTRIBUTING.md b/CONTRIBUTING.md
index a01c8c0e49..304a983d2c 100644
--- a/CONTRIBUTING.md
+++ b/CONTRIBUTING.md
@@ -174,6 +174,7 @@ license your work under the terms of the [MIT License](LICENSE.md).
 - Series of classes for a component should include a base class (e.g., `.component`) and use the base class as a prefix for modifier and sub-components (e.g., `.component-lg`).
 - Avoid inheritance and over nesting—use single, explicit classes whenever possible.
 - When feasible, default color palettes should comply with [WCAG color contrast guidelines](http://www.w3.org/TR/WCAG20/#visual-audio-contrast).
+- Except in rare cases, don't remove default `:focus` styles (via e.g. `outline: none;`) without providing alternative styles. See [this A11Y Project post](http://a11yproject.com/posts/never-remove-css-outlines/) for more details.
 
 ### JS