diff --git a/MeasurementProtocol.php b/MeasurementProtocol.php
index 57d8143..9d5e140 100644
--- a/MeasurementProtocol.php
+++ b/MeasurementProtocol.php
@@ -29,7 +29,7 @@ class MeasurementProtocol extends BaseObject
     /** @var bool Use asynchronous requests (not waiting for a response) */
     public $asyncMode = false;
 
-    /** @var bool Try to set ClientId automatically from `ga_` cookie */
+    /** @var bool Try to set ClientId automatically from `_ga` cookie */
     public $autoSetClientId = false;
 
     /**
@@ -65,9 +65,9 @@ public function request()
      */
     protected function extractClientIdFromCookie()
     {
-        $cookie = \Yii::$app->request->cookies->getValue('ga_', '');
+        $cookie = \Yii::$app->request->cookies->getValue('_ga', '');
         $cookieParts = explode('.', $cookie);
         $clientIdParts =  array_slice($cookieParts, -2);
         return implode('.', $clientIdParts);
     }
-}
\ No newline at end of file
+}
diff --git a/README.md b/README.md
index 71ab732..838bbf5 100644
--- a/README.md
+++ b/README.md
@@ -48,7 +48,7 @@ Versions in 1.* range are incompatible with PHP 7.2, use 2.* with Yii 2.0.13+ in
            'overrideIp' => false, // By default, IP is overridden by the user’s one, but you can disable this
            'anonymizeIp' => true, // If you want to anonymize the sender’s IP address
            'asyncMode' => true, // Enables the asynchronous mode (see below)
-           'autoSetClientId' => true, // Try to set ClientId automatically from the “ga_” cookie (disabled by default)
+           'autoSetClientId' => true, // Try to set ClientId automatically from the “_ga” cookie (disabled by default)
        ],
    ],
    ```
@@ -146,3 +146,16 @@ before sending the hit:
     ->setAsyncRequest(true)
     ->sendPageview();
 ```
+
+Auto set clientId from cookie
+-----------------------------
+If you set `autoSetClientId` to `true` durning component configuration you must disable `enableCookieValidation`.
+You can do this by configuring `request` component. Otherwise, the auto set clientId will not work.
+
+```php
+'components' => [
+    'request' => [
+        'enableCookieValidation' => false,
+    ],
+]
+```