diff --git a/src/Form/CheckboxWidgetForm.php b/src/Form/CheckboxWidgetForm.php
index 779052c..827d645 100644
--- a/src/Form/CheckboxWidgetForm.php
+++ b/src/Form/CheckboxWidgetForm.php
@@ -130,10 +130,11 @@ class CheckboxWidgetForm implements BaseFormIdInterface {
     // symfony class that requires a full URL.
     if (count($active_results) > 0) {
       $arguments = [];
+      $filter_key = $facet->getFacetSourceConfig()->getFilterKey();
 
       /** @var \Drupal\facets\Result\ResultInterface $link */
       foreach ($active_results as $k => $link) {
-        $arguments[] = 'f[' . $k . ']=' . $facet->getUrlAlias() . ':' . $link->getRawValue();
+        $arguments[] = $filter_key . '[' . $k . ']=' . $facet->getUrlAlias() . ':' . $link->getRawValue();
       }
 
       $url = $base_request_uri . '?' . implode('&', $arguments);
diff --git a/src/Tests/WidgetIntegrationTest.php b/src/Tests/WidgetIntegrationTest.php
index 103a598..c599039 100644
--- a/src/Tests/WidgetIntegrationTest.php
+++ b/src/Tests/WidgetIntegrationTest.php
@@ -144,6 +144,17 @@ class WidgetIntegrationTest extends WebTestBase {
   }
 
   /**
+   * Tests submitting multiple items at the same time.
+   *
+   * This uses a configured facet source url.
+   */
+  public function testMultipleCheckboxItems2() {
+    $this->drupalGet('admin/config/search/facets/facet-sources/search_api_views:search_api_test_view:page_1/edit');
+    $this->drupalPostForm(NULL, ['filter_key' => 'q'], $this->t('Save'));
+    $this->testMultipleCheckboxItems();
+  }
+
+  /**
    * Tests multiple checkbox widgets.
    */
   public function testMultipleCheckboxWidget() {