diff --git a/includes/common.inc b/includes/common.inc
index 34fa9b9..c18fcce 100644
--- a/includes/common.inc
+++ b/includes/common.inc
@@ -856,8 +856,10 @@ function drupal_http_request($url, array $options = array()) {
       // Make the socket connection to a proxy server.
       $socket = 'tcp://' . $proxy_server . ':' . variable_get('proxy_port', 8080);
       // The Host header still needs to match the real request.
-      $options['headers']['Host'] = $uri['host'];
-      $options['headers']['Host'] .= isset($uri['port']) && $uri['port'] != 80 ? ':' . $uri['port'] : '';
+      if (!isset($options['headers']['Host'])) {
+        $options['headers']['Host'] = $uri['host'];
+        $options['headers']['Host'] .= isset($uri['port']) && $uri['port'] != 80 ? ':' . $uri['port'] : '';
+      }
       break;
 
     case 'http':
@@ -867,14 +869,18 @@ function drupal_http_request($url, array $options = array()) {
       // RFC 2616: "non-standard ports MUST, default ports MAY be included".
       // We don't add the standard port to prevent from breaking rewrite rules
       // checking the host that do not take into account the port number.
-      $options['headers']['Host'] = $uri['host'] . ($port != 80 ? ':' . $port : '');
+      if (!isset($options['headers']['Host'])) {
+        $options['headers']['Host'] = $uri['host'] . ($port != 80 ? ':' . $port : '');
+      }
       break;
 
     case 'https':
       // Note: Only works when PHP is compiled with OpenSSL support.
       $port = isset($uri['port']) ? $uri['port'] : 443;
       $socket = 'ssl://' . $uri['host'] . ':' . $port;
-      $options['headers']['Host'] = $uri['host'] . ($port != 443 ? ':' . $port : '');
+      if (!isset($options['headers']['Host'])) {
+        $options['headers']['Host'] = $uri['host'] . ($port != 443 ? ':' . $port : '');
+      }
       break;
 
     default: