diff --git a/src/ExecutionClosure.php b/src/ExecutionClosure.php
index 837e931b..5ae354ac 100644
--- a/src/ExecutionClosure.php
+++ b/src/ExecutionClosure.php
@@ -18,7 +18,7 @@ class ExecutionClosure
 {
     const NOOP_INPUT = 'return null;';
 
-    private $closure;
+    private \Closure $closure;
 
     /**
      * @param Shell $__psysh__