diff --git a/modules/core_search_facets/src/Plugin/facets/facet_source/CoreNodeSearchFacetSource.php b/modules/core_search_facets/src/Plugin/facets/facet_source/CoreNodeSearchFacetSource.php
index a7b3a7a..566e521 100644
--- a/modules/core_search_facets/src/Plugin/facets/facet_source/CoreNodeSearchFacetSource.php
+++ b/modules/core_search_facets/src/Plugin/facets/facet_source/CoreNodeSearchFacetSource.php
@@ -111,7 +111,7 @@ class CoreNodeSearchFacetSource extends FacetSourcePluginBase implements CoreSea
   /**
    * {@inheritdoc}
    */
-  public function fillFacetsWithResults($facets) {
+  public function fillFacetsWithResults(array $facets) {
     foreach ($facets as $facet) {
       $configuration = array(
         'query' => NULL,
diff --git a/src/FacetSource/FacetSourcePluginInterface.php b/src/FacetSource/FacetSourcePluginInterface.php
index 632a89d..33fc849 100644
--- a/src/FacetSource/FacetSourcePluginInterface.php
+++ b/src/FacetSource/FacetSourcePluginInterface.php
@@ -23,7 +23,7 @@ interface FacetSourcePluginInterface extends PluginFormInterface, DependentPlugi
    * @param \Drupal\facets\FacetInterface[] $facets
    *   The configured facets.
    */
-  public function fillFacetsWithResults($facets);
+  public function fillFacetsWithResults(array $facets);
 
   /**
    * Returns the allowed query types for a given facet for the facet source.
diff --git a/src/Plugin/facets/facet_source/SearchApiViews.php b/src/Plugin/facets/facet_source/SearchApiViews.php
index 6cc7367..a1586c7 100644
--- a/src/Plugin/facets/facet_source/SearchApiViews.php
+++ b/src/Plugin/facets/facet_source/SearchApiViews.php
@@ -95,7 +95,7 @@ class SearchApiViews extends SearchApiBaseFacetSource implements SearchApiFacetS
   /**
    * {@inheritdoc}
    */
-  public function fillFacetsWithResults($facets) {
+  public function fillFacetsWithResults(array $facets) {
     // Check if there are results in the static cache.
     $results = $this->searchApiQueryHelper->getResults($this->pluginId);