diff --git a/core/lib/Drupal/Core/Field/Plugin/Field/FieldType/EntityReferenceItem.php b/core/lib/Drupal/Core/Field/Plugin/Field/FieldType/EntityReferenceItem.php
index bd164a9..7aaf80d 100644
--- a/core/lib/Drupal/Core/Field/Plugin/Field/FieldType/EntityReferenceItem.php
+++ b/core/lib/Drupal/Core/Field/Plugin/Field/FieldType/EntityReferenceItem.php
@@ -350,6 +350,19 @@ public static function onDependencyRemoval(FieldDefinitionInterface $field_defin
             if (isset($dependencies[$bundle->getConfigDependencyKey()][$bundle->getConfigDependencyName()])) {
               unset($handler_settings['target_bundles'][$bundle->id()]);
               $bundles_changed = TRUE;
+
+              // In case we deleted the only target bundle allowed by the field we
+              // have to log a warning message because the field will not function
+              // correctly anymore.
+              if ($handler_settings['target_bundles'] === []) {
+                \Drupal::logger('entity_reference')->critical('The %target_bundle bundle (entity type: %target_entity_type) was deleted. As a result, the %field_name entity reference field (entity_type: %entity_type, bundle: %bundle) no longer has any valid bundle it can reference. The field is not working correctly anymore and has to be adjusted.', [
+                  '%target_bundle' => $bundle->label(),
+                  '%target_entity_type' => $bundle->getEntityType()->getBundleOf(),
+                  '%field_name' => $field_definition->getName(),
+                  '%entity_type' => $field_definition->getTargetEntityTypeId(),
+                  '%bundle' => $field_definition->getTargetBundle()
+                ]);
+              }
             }
           }
         }
diff --git a/core/modules/entity_reference/entity_reference.module b/core/modules/entity_reference/entity_reference.module
index d24bac3..cd9e1d7 100644
--- a/core/modules/entity_reference/entity_reference.module
+++ b/core/modules/entity_reference/entity_reference.module
@@ -242,6 +242,11 @@ function entity_reference_entity_bundle_rename($entity_type_id, $bundle_old, $bu
 
 /**
  * Implements hook_entity_bundle_delete().
+ *
+ * We are duplicating the work done by
+ * \Drupal\Core\Field\Plugin\Field\FieldType\EntityReferenceItem::onDependencyRemoval()
+ * because we need to take into account bundles that are not provided by a
+ * config entity type so they are not part of the config dependencies.
  */
 function entity_reference_entity_bundle_delete($entity_type_id, $bundle) {
   // Gather a list of all entity reference fields.