=== modified file 'includes/common.inc'
--- includes/common.inc	2008-08-17 11:08:23 +0000
+++ includes/common.inc	2008-08-19 11:35:16 +0000
@@ -2514,6 +2514,8 @@ function page_set_cache() {
     // This will fail in some cases, see page_get_cache() for the explanation.
     if ($data = ob_get_contents()) {
       $cache = TRUE;
+      header('Content-Length: '. strlen($data));
+      header('ETag: '. md5($data));
       if (variable_get('page_compression', TRUE) && function_exists('gzencode')) {
         // We do not store the data in case the zlib mode is deflate.
         // This should be rarely happening.