diff --git a/src/Form/FacetSourceConfigForm.php b/src/Form/FacetSourceConfigForm.php
index 01bee8d4ceda632da3bc7e861681792cac0dc2d2..198af1985a6792ba2b3035b15b9034c1f90a113f 100644
--- a/src/Form/FacetSourceConfigForm.php
+++ b/src/Form/FacetSourceConfigForm.php
@@ -34,12 +34,13 @@ class FacetSourceConfigForm extends ConfigFormBase {
    */
   public function buildForm(array $form, FormStateInterface $form_state) {
     $config = $this->config('facetapi.facet_source');
+    $facet_source_id = $this->getRequest()->get('source_id');
+    $overridden_filter_key_config = $config->get('overrides.' . $facet_source_id . '.filter_key');
 
     $form['description'] = [
       '#markup' => $this->t('Saving this form will create a configuration override for this specific facet source. Not doing so will make sure that Facet API uses the default settings. This is an advanced feature and unless you are fully aware of why you\'re creating this configuration. With a default configuration of Facet API you can leave the default configuration.')
     ];
 
-    $facet_source_id = $this->getRequest()->get('source_id');
     $form['facet_source_id'] = [
       '#type' => 'hidden',
       '#value' => $facet_source_id,
@@ -51,7 +52,7 @@ class FacetSourceConfigForm extends ConfigFormBase {
       '#title' => $this->t('Filter key'),
       '#size' => 20,
       '#maxlength' => 255,
-      '#default_value' => (!is_null($config->get('overrides.' . $facet_source_id . '.filter_key')) ? $config->get('overrides.' . $facet_source_id . '.filter_key') : $config->get('filter_key')),
+      '#default_value' => (!is_null($overridden_filter_key_config) ? $overridden_filter_key_config : $config->get('filter_key')),
       '#description' => $this->t('They key used for filtering in the URL, defaults to f. You should change this to something else if you expect to have multiple facet sources on one page.'),
     ];
 
@@ -68,6 +69,9 @@ class FacetSourceConfigForm extends ConfigFormBase {
 
     $configKey = 'overrides.' . $form_state->getValue('facet_source_id') . '.';
 
+    // When saving the config, make sure it's saved in the
+    // 'overrides.facetsourceid.*' config name, so we can make sure that config
+    // is possible to be overridden per facet source.
     $config = $this->config('facetapi.facet_source');
     $config->set($configKey. 'filter_key', $form_state->getValue('filter_key'));
     $config->save();
diff --git a/src/Processor/UrlProcessorPluginBase.php b/src/Processor/UrlProcessorPluginBase.php
index 1589216a7c6b3dc2f2687d9b74002f4343b8c39b..c9fd324a8f05732441d03fd6d978614d075bb96a 100644
--- a/src/Processor/UrlProcessorPluginBase.php
+++ b/src/Processor/UrlProcessorPluginBase.php
@@ -49,7 +49,6 @@ abstract class UrlProcessorPluginBase extends ProcessorPluginBase implements Url
     parent::__construct($configuration, $plugin_id, $plugin_definition);
     $this->request = $request;
 
-    /** @var \Drupal\facetapi\FacetInterface[] $configuration */
     $facetSourceId = $configuration['facet']->getFacetSourceId();
 
     $facetSourceConfig = $config_factory->get('facetapi.facet_source');