diff --git a/src/TagField.php b/src/TagField.php
index 80df94e..f280634 100644
--- a/src/TagField.php
+++ b/src/TagField.php
@@ -403,7 +403,7 @@ class TagField extends MultiSelectField
         }
 
         if ($values instanceof DataObject && $values->exists()) {
-            return [$values->{$this->getTitleField()}];
+            return [$values->{$this->getTitleField()} ?? $values->ID];
         }
 
         if (is_int($values)) {