diff --git a/core/modules/views/src/Plugin/EntityReferenceSelection/ViewsSelection.php b/core/modules/views/src/Plugin/EntityReferenceSelection/ViewsSelection.php
index ae59751..e2e6087 100644
--- a/core/modules/views/src/Plugin/EntityReferenceSelection/ViewsSelection.php
+++ b/core/modules/views/src/Plugin/EntityReferenceSelection/ViewsSelection.php
@@ -261,7 +261,39 @@ class ViewsSelection extends PluginBase implements SelectionInterface, Container
    * {@inheritdoc}
    */
   public function validateAutocompleteInput($input, &$element, FormStateInterface $form_state, $form, $strict = TRUE) {
-    return NULL;
+    $bundled_entities = $this->getReferenceableEntities($input, '=', 6);
+    $entities = array();
+    foreach ($bundled_entities as $entities_list) {
+      $entities += $entities_list;
+    }
+    $params = array(
+      '%value' => $input,
+      '@value' => $input,
+    );
+    if (empty($entities)) {
+      if ($strict) {
+        // Error if there are no entities available for a required field.
+        $form_state->setError($element, $this->t('There are no entities matching "%value".', $params));
+      }
+    }
+    elseif (count($entities) > 5) {
+      $params['@id'] = key($entities);
+      // Error if there are more than 5 matching entities.
+      $form_state->setError($element, $this->t('Many entities are called %value. Specify the one you want by appending the id in parentheses, like "@value (@id)".', $params));
+    }
+    elseif (count($entities) > 1) {
+      // More helpful error if there are only a few matching entities.
+      $multiples = array();
+      foreach ($entities as $id => $name) {
+        $multiples[] = $name . ' (' . $id . ')';
+      }
+      $params['@id'] = $id;
+      $form_state->setError($element, $this->t('Multiple entities match this reference; "%multiple". Specify the one you want by appending the id in parentheses, like "@value (@id)".', array('%multiple' => implode('", "', $multiples))));
+    }
+    else {
+      // Take the one and only matching entity.
+      return key($entities);
+    }
   }
 
   /**