diff --git a/core/lib/Drupal/Core/EventSubscriber/RedirectLeadingSlashes.php b/core/lib/Drupal/Core/EventSubscriber/RedirectLeadingSlashes.php
index 593eaed..41f6377 100644
--- a/core/lib/Drupal/Core/EventSubscriber/RedirectLeadingSlashes.php
+++ b/core/lib/Drupal/Core/EventSubscriber/RedirectLeadingSlashes.php
@@ -25,13 +25,19 @@ class RedirectLeadingSlashes implements EventSubscriberInterface {
    */
   public function redirect(GetResponseEvent $event) {
     $request = $event->getRequest();
-    $request_uri = $request->getRequestUri();
+    // Get the requested path minus the base path.
+    $path = $request->getPathInfo();
+
     // It is impossible to create a link or a route to a path starting with
     // leading slashes. However if a form is added to the 404 page that submits
     // back to the same URI this presents an open redirect vulnerability.
-    if (strpos($request_uri, '//') === 0) {
-      $request_uri = '/' . ltrim($request_uri, '/');
-      $event->setResponse(new RedirectResponse($request->getUriForPath($request_uri)));
+    if (strpos($path, '//') === 0) {
+      $path = '/' . ltrim($path, '/');
+      $qs = $request->getQueryString();
+      if ($qs) {
+        $qs = '?' . $qs;
+      }
+      $event->setResponse(new RedirectResponse($request->getUriForPath($path) . $qs));
     }
   }
 
diff --git a/core/modules/system/src/Tests/Routing/RouterTest.php b/core/modules/system/src/Tests/Routing/RouterTest.php
index e8a46ff..b945676 100644
--- a/core/modules/system/src/Tests/Routing/RouterTest.php
+++ b/core/modules/system/src/Tests/Routing/RouterTest.php
@@ -258,13 +258,14 @@ public function testLeadingSlashes() {
     $url = $request->getUriForPath('//router_test/test1');
     $this->drupalGet($url);
     $this->assertEqual(1, $this->redirectCount, $url . " redirected to " . $this->url);
-    $this->assertUrl($this->container->get('url_generator')->generateFromPath('router_test/test1'));
+    $this->assertUrl($request->getUriForPath('/router_test/test1'));
 
-    // It should not matter how many leading slashes are used.
-    $url = $request->getUriForPath('/////////////////////////////////////////////////router_test/test1');
+    // It should not matter how many leading slashes are used and query strings
+    // should be preserved.
+    $url = $request->getUriForPath('/////////////////////////////////////////////////router_test/test1') . '?qs=test';
     $this->drupalGet($url);
     $this->assertEqual(1, $this->redirectCount, $url . " redirected to " . $this->url);
-    $this->assertUrl($this->container->get('url_generator')->generateFromPath('router_test/test1'));
+    $this->assertUrl($request->getUriForPath('/router_test/test1') . '?qs=test');
   }
 
 }