diff --git a/core/includes/common.inc b/core/includes/common.inc
index 48e6490..8ac8707 100644
--- a/core/includes/common.inc
+++ b/core/includes/common.inc
@@ -729,6 +729,17 @@ function drupal_goto($path = '', array $options = array(), $http_response_code =
  *   - data: A string containing the response body that was received.
  */
 function drupal_http_request($url, array $options = array()) {
+  // Allow an alternate HTTP client library to replace Drupal's default
+  // implementation.
+  $alternate_http_system = &drupal_static(__FUNCTION__);
+  if (!isset($alternate_http_system)) {
+    $class = variable_get('http_system');
+    $alternate_http_system = $class ? new $class() : FALSE;
+  }
+  if ($alternate_http_system) {
+    return $alternate_http_system->request($url, $options);
+  }
+
   $result = new stdClass();
 
   // Parse the URL and make sure we can handle the schema.