Index: includes/bootstrap.inc
--- includes/bootstrap.inc.orig	2008-02-11 15:36:21 +0100
+++ includes/bootstrap.inc	2008-04-09 20:47:49 +0200
@@ -272,6 +272,7 @@
  */
 function conf_init() {
   global $base_url, $base_path, $base_root;
+  global $base_url_local;
 
   // Export the following settings.php variables to the global namespace
   global $db_url, $db_prefix, $cookie_domain, $conf, $installed_profile, $update_free_access;
@@ -723,9 +724,22 @@
  * generate an equivalent using other environment variables.
  */
 function request_uri() {
+  global $base_url;
+  global $base_url_local;
 
   if (isset($_SERVER['REQUEST_URI'])) {
     $uri = $_SERVER['REQUEST_URI'];
+    if (isset($base_url) && isset($base_url_local)) {
+      $parts = parse_url($base_url_local);
+      if (   strlen($uri) >= strlen($base_url_local)
+          && substr($uri, 0, strlen($base_url_local)) == $base_url_local) {
+        $uri = $base_url .  substr($uri, strlen($base_url_local));
+      }
+      elseif (   strlen($uri) >= strlen($parts["path"])
+          && substr($uri, 0, strlen($parts["path"])) == $parts["path"]) {
+        $uri = $base_url .  substr($uri, strlen($parts["path"]));
+      }
+    }
   }
   else {
     if (isset($_SERVER['argv'])) {
Index: sites/default/default.settings.php
--- sites/default/default.settings.php.orig	2007-12-20 10:35:10 +0100
+++ sites/default/default.settings.php	2008-04-09 20:47:32 +0200
@@ -126,6 +126,24 @@
 # $base_url = 'http://www.example.com';  // NO trailing slash!
 
 /**
+ * Local Base URL (optional).
+ *
+ * If you are running Drupal behind a reverse proxy, $base_url (see above)
+ * usually points to the URL of the reverse proxy. Drupal uses this for
+ * all sorts of external URLs. In order to correctly calculate sub-URLs
+ * below $base_url for embedded HTML forms, Drupal also has to know the
+ * URL on the local/origin server under which Drupal is contacted by the
+ * reverse proxy. This is what $base_url_local is for.
+ *
+ * Examples:
+ *   $base_url_local = 'http://www.example.com:8080/drupal';
+ *
+ * It is not allowed to have a trailing slash; Drupal will add it
+ * for you.
+ */
+# $base_url_local = 'http://www.example.com:8080/drupal';  // NO trailing slash!
+
+/**
  * PHP settings:
  *
  * To see what PHP settings are possible, including whether they can