diff --git a/core/lib/Drupal/Component/Utility/UrlHelper.php b/core/lib/Drupal/Component/Utility/UrlHelper.php
index e8194c44f7..a9a4a68fa4 100644
--- a/core/lib/Drupal/Component/Utility/UrlHelper.php
+++ b/core/lib/Drupal/Component/Utility/UrlHelper.php
@@ -188,7 +188,7 @@ public static function parse($url) {
    * although this is deprecated. Because variables in PHP cannot have periods
    * and spaces in their names, parse_str() converts them to underscores. This
    * breaks external links and front end libraries that require specific
-   * parameter names.
+   * parameter names. It can also cause name collisions.
    *
    * @param string $query
    *   A query string to parse.
@@ -197,22 +197,22 @@ public static function parse($url) {
    *   The result of parse_str() with original parameter names restored.
    */
   public static function parseQueryString($query) {
-    // Create an array to map parsed parameter names to original names.
-    $names = [];
+    // Create an array to map parsed parameters to original names.
+    $parsed = [];
     foreach (explode('&', $query) as $param) {
       list($name) = explode('=', $param, 2);
       $name = strstr($name, '[', true) ?: $name;
-      parse_str($name, $parsed);
-      $names[key($parsed)] = $name;
-    }
-    // Parse the query string.
-    parse_str($query, $query);
-    // Replaced changed parameter names with original names.
-    foreach (array_diff($names, array_keys($query)) as $parsed => $name) {
-      $query[$name] = $query[$parsed];
-      unset($query[$parsed]);
+      // Parse the query parameter.
+      parse_str($param, $param);
+      // Merge the parameter into the parsed array.
+      if (isset($parsed[$name])) {
+        $parsed[$name] = array_merge($parsed[$name], reset($param));
+      }
+      else {
+        $parsed[$name] = reset($param);
+      }
     }
-    return $query;
+    return $parsed;
   }
 
   /**
diff --git a/core/tests/Drupal/Tests/Component/Utility/UrlHelperTest.php b/core/tests/Drupal/Tests/Component/Utility/UrlHelperTest.php
index 572c7dc48a..c446eeec93 100644
--- a/core/tests/Drupal/Tests/Component/Utility/UrlHelperTest.php
+++ b/core/tests/Drupal/Tests/Component/Utility/UrlHelperTest.php
@@ -269,26 +269,25 @@ public static function providerTestParse() {
           'fragment' => 'footer',
         ],
       ],
-      [
-        'http://www.example.com/my/path?my.destination=my.home&my destination=my home&my_destination[]=my.home&my_destination[]=my_home&my_destination[]=home',
+      'query parameters with characters not allowed in PHP variable names' => [
+        'http://www.example.com/my/path?single.value=&single value=&single_value=&multi.value[first]=&multi.value[second]=&multi value[third]=&multi value[fourth]=&multi_value[fifth]=&multi_value[sixth]=',
         [
           'path' => 'http://www.example.com/my/path',
           'query' => [
-            'my_destination' => ['my.home', 'my_home', 'home'],
-          ],
-          'fragment' => '',
-        ],
-      ],
-      [
-        'http://www.example.com/my/path?param[nested][0]=value&param[nested][1]=2ndvalue',
-        [
-          'path' => 'http://www.example.com/my/path',
-          'query' => [
-            'param' => [
-              'nested' => [
-                0 => 'value',
-                1 => '2ndvalue',
-              ],
+            'single.value' => '',
+            'single value' => '',
+            'single_value' => '',
+            'multi.value' => [
+              'first' => '',
+              'second' => '',
+            ],
+            'multi value' => [
+              'third' => '',
+              'fourth' => '',
+            ],
+            'multi_value' => [
+              'fifth' => '',
+              'sixth' => '',
             ],
           ],
           'fragment' => '',
diff --git a/core/tests/Drupal/Tests/Core/UrlTest.php b/core/tests/Drupal/Tests/Core/UrlTest.php
index 99603fffce..2e8442ab0e 100644
--- a/core/tests/Drupal/Tests/Core/UrlTest.php
+++ b/core/tests/Drupal/Tests/Core/UrlTest.php
@@ -339,8 +339,8 @@ public function testGetUriForExternalUrl() {
    * @covers ::getUri
    */
   public function testGetUriForExternalUrlWithParameters() {
-    $url = Url::fromUri('http://www.example.com/my/path?my.destination=my.home&my destination=my home&my_destination[]=my.home&my_destination[]=my_home&my_destination[]=home');
-    $this->assertEquals('http://www.example.com/my/path?my.destination=my.home&my destination=my home&my_destination[]=my.home&my_destination[]=my_home&my_destination[]=home', $url->getUri());
+    $url = Url::fromUri('http://www.example.com/my/path?single.value=&single value=&single_value=&multi.value[first]=&multi.value[second]=&multi value[third]=&multi value[fourth]=&multi_value[fifth]=&multi_value[sixth]=');
+    $this->assertEquals('http://www.example.com/my/path?single.value=&single value=&single_value=&multi.value[first]=&multi.value[second]=&multi value[third]=&multi value[fourth]=&multi_value[fifth]=&multi_value[sixth]=', $url->getUri());
   }
 
   /**