diff --git a/docs/contributing.rst b/docs/contributing.rst
index 100f13f..a8010a9 100644
--- a/docs/contributing.rst
+++ b/docs/contributing.rst
@@ -28,6 +28,7 @@
 * If somehow the tests get into a failing state on ``master`` (such as by a
   backwards incompatible release of a dependency) no pull requests may be
   merged until this is rectified.
+* All merged patches must have 100% test coverage.
 
 The purpose of these policies is to minimize the chances we merge a change
 which jeopardizes our users' security.