diff --git a/src/pocketmine/utils/Utils.php b/src/pocketmine/utils/Utils.php
index 0757a282e..244784165 100644
--- a/src/pocketmine/utils/Utils.php
+++ b/src/pocketmine/utils/Utils.php
@@ -105,7 +105,8 @@ use const STR_PAD_RIGHT;
  * Big collection of functions
  */
 class Utils{
-	public static $os;
+	/** @var string */
+	private static $os;
 	/** @var UUID|null */
 	private static $serverUniqueId = null;