diff --git a/apache/lib/common b/apache/lib/common
index 9c329e4..fd9594c 100644
--- a/apache/lib/common
+++ b/apache/lib/common
@@ -720,7 +720,8 @@ $(__vhost_creds_statement "$cfg" "$dest" | prefix "        ")
 $([ "$protocol" == "https" ] && echo "    SSLProxyEngine On")
 </IfModule>
 
-RequestHeader set "X-Forwarded-Proto" "$protocol"
+SetEnvIf X-Forwarded-Proto "^$" forwarded_proto_not_set=true
+RequestHeader set "X-Forwarded-Proto" "$protocol" env=forwarded_proto_not_set
 
 ## Fix IE problem (httpapache proxy dav error 408/409)
 SetEnv proxy-nokeepalive 1