diff --git a/src/Selenium2Driver.php b/src/Selenium2Driver.php
index a805ac5a..54e87d5f 100755
--- a/src/Selenium2Driver.php
+++ b/src/Selenium2Driver.php
@@ -979,7 +979,9 @@ public function resizeWindow(int $width, int $height, ?string $name = null)
             );
         }
         else {
-            $this->wdSession->window($name ? $name : 'current')->postSize(
+            $window = $this->getWebDriverSession()->window($name ?: 'current');
+            \assert($window instanceof Window);
+            $window->postSize(
                 array('width' => $width, 'height' => $height)
             );
         }