diff --git a/src/Plugin/Block/ContentEmbedBlock.php b/src/Plugin/Block/ContentEmbedBlock.php
index e03c717..20281de 100644
--- a/src/Plugin/Block/ContentEmbedBlock.php
+++ b/src/Plugin/Block/ContentEmbedBlock.php
@@ -5,6 +5,7 @@ namespace Drupal\content_browser\Plugin\Block;
 use Drupal\Component\Utility\NestedArray;
 use Drupal\Core\Block\BlockBase;
 use Drupal\Core\Form\FormStateInterface;
+use Drupal\Core\Form\SubformStateInterface;
 use Drupal\node\Entity\Node;
 
 /**
@@ -47,6 +48,16 @@ class ContentEmbedBlock extends BlockBase {
    * {@inheritdoc}
    */
   public function blockForm($form, FormStateInterface $form_state) {
+    // This method receives a sub form state instead of the full form state.
+    // There is an ongoing discussion around this which could result in the
+    // passed form state going back to a full form state. In order to prevent
+    // future breakage because of a core update we'll just check which type of
+    // FormStateInterface we've been passed and act accordingly.
+    // @See https://www.drupal.org/node/2798261
+    if ($form_state instanceof SubformStateInterface) {
+      $form_state = $form_state->getCompleteFormState();
+    }
+
     $entities = $form_state->getValue([
       'settings',
       'selection',