diff --git a/CONTRIBUTING.md b/CONTRIBUTING.md
index a7b21dcd8786..1fe3d2c0993a 100644
--- a/CONTRIBUTING.md
+++ b/CONTRIBUTING.md
@@ -109,6 +109,9 @@ which consist mainly of a reference to
 [PEP 8](https://www.python.org/dev/peps/pep-0008/) -- for the code you
 put in the pull request.
 
+Also, do not squash your commits after you have submitted a pull request, as this
+erases context during review. We will squash commits when the pull request is merged.
+
 You may also find other pages in the
 [Mypy developer guide](https://github.com/python/mypy/wiki/Developer-Guides)
 helpful in developing your change.