diff --git a/code/TestSessionEnvironment.php b/code/TestSessionEnvironment.php
index 1aa44f7..347961d 100644
--- a/code/TestSessionEnvironment.php
+++ b/code/TestSessionEnvironment.php
@@ -299,7 +299,9 @@ class TestSessionEnvironment extends Object {
 		} else {
 			$content = json_encode($state);
 		}
+		$old = umask(0);
 		file_put_contents($this->getFilePath(), $content, LOCK_EX);
+		umask($old);
 	}
 
 	public function loadFromFile() {