diff --git a/README.md b/README.md
index d54e14c..685dd70 100644
--- a/README.md
+++ b/README.md
@@ -200,7 +200,7 @@ steps:
 - **Observability**: Add metadata for logging, monitoring, and debugging
 - **Routing**: Control request routing through custom gateways or load balancers
 
-**Header name requirements**: Header names must contain only alphanumeric characters and hyphens (following RFC 7230). Underscores and other special characters are not allowed.
+**Header name requirements**: Header names must follow the HTTP token syntax defined in RFC 7230 (which permits underscores). For maximum compatibility with intermediaries and tooling, we recommend using only alphanumeric characters and hyphens.
 
 **Security note**: Always use GitHub secrets for sensitive header values like API keys, tokens, or passwords. The action automatically masks common sensitive headers (containing `key`, `token`, `secret`, `password`, or `authorization`) in logs.