diff --git a/includes/bootstrap.inc b/includes/bootstrap.inc
index 9c2e4bad2eb1030cddc2d06548160b629de02eaf..299f9059fbf301f6446aae491538c7ebbc2586e5 100644
--- a/includes/bootstrap.inc
+++ b/includes/bootstrap.inc
@@ -308,6 +308,9 @@ function drupal_initialize_variables() {
   if (!isset($_SERVER['HTTP_REFERER'])) {
     $_SERVER['HTTP_REFERER'] = '';
   }
+  if (!isset($_SERVER['SERVER_PROTOCOL']) || ($_SERVER['SERVER_PROTOCOL'] != 'HTTP/1.0' && $_SERVER['SERVER_PROTOCOL'] != 'HTTP/1.1')) {
+    $_SERVER['SERVER_PROTOCOL'] = 'HTTP/1.0';
+  }
 }
 
 /**
@@ -640,7 +643,7 @@ 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: $etag");
     exit();
@@ -1020,7 +1023,7 @@ function _drupal_bootstrap($phase) {
     case DRUPAL_BOOTSTRAP_ACCESS:
       // Deny access to blocked IP addresses - t() is not yet available.
       if (drupal_is_denied(ip_address())) {
-        header('HTTP/1.1 403 Forbidden');
+        header($_SERVER['SERVER_PROTOCOL'] . ' 403 Forbidden');
         print 'Sorry, ' . check_plain(ip_address()) . ' has been banned.';
         exit();
       }
diff --git a/includes/common.inc b/includes/common.inc
index 13628d2f1f7d9a045c0b626d5470605a170efa48..81e2ca1cd68369d43cc65fc80407b3522f629c95 100644
--- a/includes/common.inc
+++ b/includes/common.inc
@@ -325,7 +325,7 @@ function drupal_goto($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 offline'));
   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'))))));
@@ -335,7 +335,7 @@ 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);
 
@@ -365,7 +365,7 @@ 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);
 
   // Keep old path for reference.
diff --git a/includes/database/database.inc b/includes/database/database.inc
index 2dafd3d2e607b24d95e222892610b97594be1d09..ed479fe5aa84d06aa40dc73c71824b2b4f9b1bc0 100644
--- a/includes/database/database.inc
+++ b/includes/database/database.inc
@@ -1780,7 +1780,7 @@ function db_change_field(&$ret, $table, $field, $field_new, $spec, $keys_new = a
 function _db_error_page($error = '') {
   global $db_type;
   drupal_maintenance_theme();
-  drupal_set_header('HTTP/1.1 503 Service Unavailable');
+  drupal_set_header($_SERVER['SERVER_PROTOCOL'] . ' 503 Service Unavailable');
   drupal_set_title('Site offline');
 }
 
diff --git a/install.php b/install.php
index 0ff2573bbc156e526e424e5c32f6d57593627993..35d34d8f32b09d263b06a9a32cfe27753c47760f 100644
--- a/install.php
+++ b/install.php
@@ -24,7 +24,7 @@ function install_main() {
   // running tests.  However, for security reasons, it is imperative that no
   // installation be permitted using such a prefix.
   if (preg_match("/^simpletest\d+$/", $_SERVER['HTTP_USER_AGENT'])) {
-    header('HTTP/1.1 403 Forbidden');
+    header($_SERVER['SERVER_PROTOCOL'] . ' 403 Forbidden');
     exit;
   }