diff --git a/core/lib/Drupal/Core/Database/Query/SelectExtender.php b/core/lib/Drupal/Core/Database/Query/SelectExtender.php
index cca68c7287f..0c253de704e 100644
--- a/core/lib/Drupal/Core/Database/Query/SelectExtender.php
+++ b/core/lib/Drupal/Core/Database/Query/SelectExtender.php
@@ -338,6 +338,9 @@ class SelectExtender implements SelectInterface {
     return $this;
   }
 
+  /**
+   * {@inheritdoc}
+   */
   public function __toString() {
     return (string) $this->query;
   }
diff --git a/core/lib/Drupal/Core/Database/Query/SelectInterface.php b/core/lib/Drupal/Core/Database/Query/SelectInterface.php
index cd4950504b7..795c0860bce 100644
--- a/core/lib/Drupal/Core/Database/Query/SelectInterface.php
+++ b/core/lib/Drupal/Core/Database/Query/SelectInterface.php
@@ -648,4 +648,12 @@ interface SelectInterface extends ConditionInterface, AlterableInterface, Extend
    */
   public function forUpdate($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();
+
 }