diff --git a/core/lib/Drupal/Core/Entity/EntityTypeInterface.php b/core/lib/Drupal/Core/Entity/EntityTypeInterface.php
index a4a3a416b2b..e148e7db4d1 100644
--- a/core/lib/Drupal/Core/Entity/EntityTypeInterface.php
+++ b/core/lib/Drupal/Core/Entity/EntityTypeInterface.php
@@ -228,8 +228,9 @@ interface EntityTypeInterface extends PluginDefinitionInterface {
    * @param string $operation
    *   The name of the operation to use, e.g., 'default'.
    *
-   * @return string
-   *   The class for this operation's form for this entity type.
+   * @return string|null
+   *   The class for this operation's form for this entity type or NULL if the
+   *   entity type does not have a form class for this operation.
    *
    * @see \Drupal\Core\Entity\EntityFormBuilderInterface
    */