diff -u b/core/modules/comment/comment.install b/core/modules/comment/comment.install
--- b/core/modules/comment/comment.install
+++ b/core/modules/comment/comment.install
@@ -57,7 +57,6 @@
         'not null' => TRUE,
         'default' => '',
         'length' => FieldStorageConfig::NAME_MAX_LENGTH,
-        'is_ascii' => TRUE,
         'description' => 'The field_name of the field that was used to add this comment.',
       ),
       'cid' => array(