diff --git a/docs/reference/filters.md b/docs/reference/filters.md
index 015f35d185..3f2e2d5548 100644
--- a/docs/reference/filters.md
+++ b/docs/reference/filters.md
@@ -115,6 +115,8 @@ Example:
 route1: * -> preserveHost("true") -> "http://backend.example.org";
 ```
 
+Default `proxyPreserveHost` behavior can be configured by `-proxy-preserve-host` flag which is `false` by default.
+
 ### modRequestHeader
 
 Replace all matched regex expressions in the given header.