diff --git a/src/Plugin/DataType/DynamicEntityReference.php b/src/Plugin/DataType/DynamicEntityReference.php
index 7793a14..285aeca 100644
--- a/src/Plugin/DataType/DynamicEntityReference.php
+++ b/src/Plugin/DataType/DynamicEntityReference.php
@@ -65,7 +65,19 @@ class DynamicEntityReference extends EntityReference {
    * {@inheritdoc}
    */
   public function getConstraints() {
-    $this->definition->addConstraint('Bundle', ['bundle' => $this->parent->parent->getSetting($this->parent->getValue()['target_type'])['handler_settings']['target_bundles']]);
+    $field = $this->parent->parent;
+    $values = $this->parent->getValue();
+    // We cannot validate the bundle until we know the target-type of this
+    // item.
+    if (isset($values['target_type'])) {
+      $target_type = $values['target_type'];
+      // Get the handler settings for the target type of this item.
+      $target_type_settings = $field->getSettings($target_type);
+      if (isset($target_type_settings['handler_settings']['target_bundles'])) {
+        // Add the constraint to limit the bundles of this item.
+        $this->definition->addConstraint('Bundle', ['bundle' => $target_type_settings['handler_settings']['target_bundles']]);
+      }
+    }
     $constraints = parent::getConstraints();
     return $constraints;
   }