diff --git a/src/GlobalSnapshot.php b/src/GlobalSnapshot.php
index a9cac1c..ef465f2 100644
--- a/src/GlobalSnapshot.php
+++ b/src/GlobalSnapshot.php
@@ -7,14 +7,14 @@
     // can be restored to this point in time by calling $this->restore();
     class GlobalSnapshot {
         // Declare all PHP superglobals
-        private array $_ENV;
-        private array $_GET;
-        private array $_POST;
-        private array $_FILES;
-        private array $_SERVER;
-        private array $_COOKIE;
-        private array $_REQUEST;
-        private array $_SESSION;
+        private readonly array $_ENV;
+        private readonly array $_GET;
+        private readonly array $_POST;
+        private readonly array $_FILES;
+        private readonly array $_SERVER;
+        private readonly array $_COOKIE;
+        private readonly array $_REQUEST;
+        private readonly array $_SESSION;
 
 		// Declare additional PHP globals (for PHP 8.0+ compatability)
 		// These will not be captured, or altered by GlobalSnapshot