diff --git a/metatag.module b/metatag.module
index f42ead9..869233e 100644
--- a/metatag.module
+++ b/metatag.module
@@ -410,12 +410,34 @@ function metatag_get_default_tags($entity = NULL) {
  * Implements hook_entity_base_field_info_alter().
  */
 function metatag_entity_base_field_info_alter(&$fields, EntityTypeInterface $entity_type) {
-  $fields['metatag'] = BaseFieldDefinition::create('map')
-    ->setName('Metatags')
+  // If the entity type doesn't have a base table then there's no point in
+  // supporting it.
+  $base_table = $entity_type->getBaseTable();
+  if (empty($base_table)) {
+    return;
+  }
+
+  // The entity type must also have a canonical route.
+  if (!$entity_type->hasLinkTemplate('canonical')) {
+    return;
+  }
+
+  // Certain classes are just not supported, end of story.
+  $original_class = $entity_type->getOriginalClass();
+  $verbotten_classes = [
+    'Drupal\comment\Entity\Comment',
+  ];
+  if (in_array($original_class, $verbotten_classes)) {
+    return;
+  }
+
+  // If the entity type hasn't been skipped above, then create the Metatag
+  // field thing.
+  $fields['metatag'] = BaseFieldDefinition::create('map')->setName('Metatags')
     ->setLabel(t('Metatags'))
     ->setDescription(t('The metatags for the entity.'))
     ->setClass('\Drupal\metatag\Plugin\Field\MetatagEntityFieldItemList')
     ->setQueryable(FALSE)
-    ->setComputed(TRUE);
+    ->setComputed(TRUE)
+    ->setTargetEntityTypeId($entity_type->id());
 }
-