diff --git a/core/lib/Drupal/Core/Database/Query/SelectExtender.php b/core/lib/Drupal/Core/Database/Query/SelectExtender.php
index cca68c7287fc4ed3ee4487cb0a9512c1ae079b6b..0c253de704e9c017dfe87b8d010f0afba137c1b3 100644
--- a/core/lib/Drupal/Core/Database/Query/SelectExtender.php
+++ b/core/lib/Drupal/Core/Database/Query/SelectExtender.php
@@ -338,6 +338,9 @@ public function notExists(SelectInterface $select) {
     return $this;
   }
 
+  /**
+   * {@inheritdoc}
+   */
   public function __toString() {
     return (string) $this->query;
   }
diff --git a/core/lib/Drupal/Core/Database/Query/SelectInterface.php b/core/lib/Drupal/Core/Database/Query/SelectInterface.php
index cd4950504b7733f257b96911d1e2abc92b61b7e8..795c0860bce025bdfc0715224adade1262b9416d 100644
--- a/core/lib/Drupal/Core/Database/Query/SelectInterface.php
+++ b/core/lib/Drupal/Core/Database/Query/SelectInterface.php
@@ -648,4 +648,12 @@ public function __clone();
    */
   public function forUpdate($set = TRUE);
 
+  /**
+   * Returns a string representation of how the query will be executed in SQL.
+   *
+   * @return string
+   *   The Select Query object expressed as a string.
+   */
+  public function __toString();
+
 }