diff --git core/modules/taxonomy/src/Plugin/views/filter/TaxonomyIndexTid.php core/modules/taxonomy/src/Plugin/views/filter/TaxonomyIndexTid.php
index 7710bae..4174bf5 100644
--- core/modules/taxonomy/src/Plugin/views/filter/TaxonomyIndexTid.php
+++ core/modules/taxonomy/src/Plugin/views/filter/TaxonomyIndexTid.php
@@ -350,7 +350,7 @@ class TaxonomyIndexTid extends ManyToOne {
     $identifier = $this->options['expose']['identifier'];
     $input = $form_state->getValue($identifier);
 
-    if ($this->options['is_grouped'] && isset($this->options['group_info']['group_items'][$input])) {
+    if ($this->options['is_grouped'] && is_string($input) && isset($this->options['group_info']['group_items'][$input])) {
       $this->validated_exposed_input = $this->options['group_info']['group_items'][$input]['value'];
       return;
     }