diff --git a/content/en/docs/concepts/services-networking/service.md b/content/en/docs/concepts/services-networking/service.md
index c5773a12af..dfaa1a0a68 100644
--- a/content/en/docs/concepts/services-networking/service.md
+++ b/content/en/docs/concepts/services-networking/service.md
@@ -267,6 +267,8 @@ spec:
     targetPort: 9377
 ```
 
+Note that the port names must only contain lowercase alphanumeric characters and `-`, and must begin & end with an alphanumeric character. `123-abc` and `web` are valid, but `123_abc` and `-web` are not valid names.
+
 ## Choosing your own IP address
 
 You can specify your own cluster IP address as part of a `Service` creation