diff --git a/includes/bootstrap.inc b/includes/bootstrap.inc
index 92e0c0f..f557fc8 100644
--- a/includes/bootstrap.inc
+++ b/includes/bootstrap.inc
@@ -378,6 +378,10 @@ function conf_init() {
   global $db_url, $db_prefix, $db_collation, $cookie_domain, $conf, $installed_profile, $update_free_access;
   $conf = array();
 
+  if (!isset($_SERVER['SERVER_PROTOCOL']) || ($_SERVER['SERVER_PROTOCOL'] != 'HTTP/1.0' && $_SERVER['SERVER_PROTOCOL'] != 'HTTP/1.1')) {
+    $_SERVER['SERVER_PROTOCOL'] = 'HTTP/1.0';
+  }
+
   if (isset($_SERVER['HTTP_HOST'])) {
     // As HTTP_HOST is user input, ensure it only contains characters allowed
     // in hostnames. See RFC 952 (and RFC 2181).
@@ -385,7 +389,7 @@ function conf_init() {
     $_SERVER['HTTP_HOST'] = strtolower($_SERVER['HTTP_HOST']);
     if (!drupal_valid_http_host($_SERVER['HTTP_HOST'])) {
       // HTTP_HOST is invalid, e.g. if containing slashes it may be an attack.
-      header('HTTP/1.1 400 Bad Request');
+      header($_SERVER['SERVER_PROTOCOL'] .' 400 Bad Request');
       exit;
     }
   }
@@ -749,7 +753,7 @@ function drupal_page_cache_header($cache) {
   if ($if_modified_since && $if_none_match
       && $if_none_match == $etag // etag must match
       && $if_modified_since == $last_modified) {  // if-modified-since must match
-    header('HTTP/1.1 304 Not Modified');
+    header($_SERVER['SERVER_PROTOCOL'] .' 304 Not Modified');
     // All 304 responses must send an etag if the 200 response for the same object contained an etag
     header("Etag: $etag");
     return;
@@ -1149,7 +1153,7 @@ function _drupal_bootstrap($phase) {
     case DRUPAL_BOOTSTRAP_ACCESS:
       // Deny access to hosts which were banned - t() is not yet available.
       if (drupal_is_denied('host', ip_address())) {
-        header('HTTP/1.1 403 Forbidden');
+        header($_SERVER['SERVER_PROTOCOL'] .' 403 Forbidden');
         print 'Sorry, '. check_plain(ip_address()) .' has been banned.';
         exit();
       }
diff --git a/includes/common.inc b/includes/common.inc
index 3d73784..76ceb53 100644
--- a/includes/common.inc
+++ b/includes/common.inc
@@ -354,7 +354,7 @@ function drupal_goto($path = '', $query = NULL, $fragment = NULL, $http_response
  */
 function drupal_site_offline() {
   drupal_maintenance_theme();
-  drupal_set_header('HTTP/1.1 503 Service unavailable');
+  drupal_set_header($_SERVER['SERVER_PROTOCOL'] .' 503 Service unavailable');
   drupal_set_title(t('Site off-line'));
   print theme('maintenance_page', filter_xss_admin(variable_get('site_offline_message',
     t('@site is currently under maintenance. We should be back shortly. Thank you for your patience.', array('@site' => variable_get('site_name', 'Drupal'))))));
@@ -364,7 +364,7 @@ function drupal_site_offline() {
  * Generates a 404 error if the request can not be handled.
  */
 function drupal_not_found() {
-  drupal_set_header('HTTP/1.1 404 Not Found');
+  drupal_set_header($_SERVER['SERVER_PROTOCOL'] .' 404 Not Found');
 
   watchdog('page not found', check_plain($_GET['q']), NULL, WATCHDOG_WARNING);
 
@@ -394,7 +394,7 @@ function drupal_not_found() {
  * Generates a 403 error if the request is not allowed.
  */
 function drupal_access_denied() {
-  drupal_set_header('HTTP/1.1 403 Forbidden');
+  drupal_set_header($_SERVER['SERVER_PROTOCOL'] .' 403 Forbidden');
 
   watchdog('access denied', check_plain($_GET['q']), NULL, WATCHDOG_WARNING);
 
diff --git a/includes/database.inc b/includes/database.inc
index 683ae69..91807da 100644
--- a/includes/database.inc
+++ b/includes/database.inc
@@ -173,7 +173,7 @@ function _db_error_page($error = '') {
   global $db_type;
   drupal_init_language();
   drupal_maintenance_theme();
-  drupal_set_header('HTTP/1.1 503 Service Unavailable');
+  drupal_set_header($_SERVER['SERVER_PROTOCOL'] .' 503 Service Unavailable');
   drupal_set_title('Site off-line');
 
   $message = '<p>The site is currently not available due to technical problems. Please try again later. Thank you for your understanding.</p>';