diff --git a/src/Evaluator/EvalCallExpression.php b/src/Evaluator/EvalCallExpression.php
index eb3b5b3..e9c1bd1 100644
--- a/src/Evaluator/EvalCallExpression.php
+++ b/src/Evaluator/EvalCallExpression.php
@@ -41,8 +41,13 @@ public function __invoke(CallExpression $callExpression): MonkeyObject
         return $this->applyFunction($monkeyObject, $args);
     }
 
-    public function applyFunction(MonkeyObject $monkeyObject, array $args): MonkeyObject
-    {
+    /**
+     * @param array<MonkeyObject> $args
+     */
+    public function applyFunction(
+        MonkeyObject $monkeyObject,
+        array $args,
+    ): MonkeyObject {
         if ($monkeyObject instanceof FunctionObject) {
             $environment = $this->extendFunctionEnv($monkeyObject, $args);