diff --git a/docs/content/middlewares/http/ratelimit.md b/docs/content/middlewares/http/ratelimit.md
index 3020edbe7..bcedbcb00 100644
--- a/docs/content/middlewares/http/ratelimit.md
+++ b/docs/content/middlewares/http/ratelimit.md
@@ -432,6 +432,8 @@ http:
 
 Name of the header used to group incoming requests.
 
+!!! important "If the header is not present, rate limiting will still be applied, but all requests without the specified header will be grouped together."
+
 ```yaml tab="Docker"
 labels:
   - "traefik.http.middlewares.test-ratelimit.ratelimit.sourcecriterion.requestheadername=username"