diff --git a/core/lib/Drupal/Core/Session/WriteSafeSessionHandler.php b/core/lib/Drupal/Core/Session/WriteSafeSessionHandler.php
index ee4275cb92..543fa86594 100644
--- a/core/lib/Drupal/Core/Session/WriteSafeSessionHandler.php
+++ b/core/lib/Drupal/Core/Session/WriteSafeSessionHandler.php
@@ -22,7 +22,8 @@ class WriteSafeSessionHandler implements \SessionHandlerInterface, WriteSafeSess
   /**
    * The read sessions.
    *
-   * @var array sessionId => session
+   * @var array
+   *   Session data keyed by the session ID.
    */
   private $readSessions;