diff --git a/docs/source/whatsnew/pr/README.md b/docs/source/whatsnew/pr/README.md
index 43e22de..b098249 100644
--- a/docs/source/whatsnew/pr/README.md
+++ b/docs/source/whatsnew/pr/README.md
@@ -11,8 +11,8 @@ script and populate [development.rst](../development.rst)
 with the contents of this directory, and clean it up.
 
 Files which describe new features can have any name, such as
-`antigravity-feature.rst`, whereas backwards incompatible changes should have a
-filename starting with `incompat-`, such as `incompat-switching-to-perl.rst`.
-Our "What's new" files always have two sections,  and this prefix scheme will
-make sure that the backwards incompatible changes get routed to their proper
-section.
+`antigravity-feature.rst`, whereas backwards incompatible changes **must have**
+have a filename starting with `incompat-`, such as
+`incompat-switching-to-perl.rst`.  Our "What's new" files always have two
+sections,  and this prefix scheme will make sure that the backwards incompatible
+changes get routed to their proper section.