diff --git a/config/policy.go b/config/policy.go
index ebdc1810d..8ef515967 100644
--- a/config/policy.go
+++ b/config/policy.go
@@ -87,6 +87,9 @@ type Policy struct {
 
 	// PreserveHostHeader disables host header rewriting.
 	//
+	// This option only takes affect if the destination is a DNS name. If the destination is an IP address,
+	// use SetRequestHeaders to explicitly set the "Host" header.
+	//
 	// https://nginx.org/en/docs/http/ngx_http_proxy_module.html#proxy_set_header
 	PreserveHostHeader bool `mapstructure:"preserve_host_header" yaml:"preserve_host_header,omitempty"`
 
diff --git a/docs/docs/upgrading.md b/docs/docs/upgrading.md
index 1ef50d07f..1b8068cbd 100644
--- a/docs/docs/upgrading.md
+++ b/docs/docs/upgrading.md
@@ -58,6 +58,14 @@ In `0.9.0`:
 option httpchk GET /ping HTTP/1.1\r\nHost:pomerium
 ```
 
+### preserve_host_header option
+
+With this release, Pomerium uses an embedded envoy proxy instead hand-written one. Thus, we defer the preserve host header
+functionality to [envoy's auto_host_rewrite](https://www.envoyproxy.io/docs/envoy/latest/api-v3/config/route/v3/route_components.proto#envoy-v3-api-field-config-route-v3-routeaction-auto-host-rewrite),
+which does not affect if the policy routes to a static IP.
+
+To preserve 0.8.x behavior, you can use the `set_request_headers` option to explicitly set the Host header.
+
 # Since 0.8.0
 
 ## Breaking