diff --git a/framework/CHANGELOG.md b/framework/CHANGELOG.md
index ea61588541..957d51d8e0 100644
--- a/framework/CHANGELOG.md
+++ b/framework/CHANGELOG.md
@@ -84,6 +84,7 @@ Yii Framework 2 Change Log
 - Enh #10158: Added the possibility to specify CSS and Javascript options per file in `\yii\web\AssetBundle` (machour)
 - Enh #10170: `Yii::powered()` now uses `Yii::t()` (SamMousa)
 - Enh #10218: Support for selecting multiple filter values with the same name was added to `yii.gridView.js` (omnilight, silverfire)
+- Enh #10255: Added Yii warning to session initialization if session was already started (AnatolyRugalev)
 - Enh #10264: Generation of HTML tags in Yii's JavaScript now uses jQuery style (silverfire)
 - Enh #10267: `yii.js` - added original event passing to `pjaxOptions` for links with `data-method` and `data-pjax` (servocoder, silverfire)
 - Enh #10319: `yii\helpers\VarDumper::dump()` now respects PHP magic method `__debugInfo()` (klimov-paul)
diff --git a/framework/web/Session.php b/framework/web/Session.php
index ce18ac3a03..0e604f6b7a 100644
--- a/framework/web/Session.php
+++ b/framework/web/Session.php
@@ -97,6 +97,9 @@ class Session extends Component implements \IteratorAggregate, \ArrayAccess, \Co
     {
         parent::init();
         register_shutdown_function([$this, 'close']);
+        if ($this->getIsActive()) {
+            Yii::warning("Session is already started", __METHOD__);
+        }
     }
 
     /**