diff --git a/src/Config.php b/src/Config.php
index dd51ce7..35c9dc2 100644
--- a/src/Config.php
+++ b/src/Config.php
@@ -86,26 +86,30 @@ public function has(string $key): bool
         return (bool) $this->get($key);
     }
 
-    public function offsetExists($offset)
+    public function offsetExists($offset): bool
     {
         return array_key_exists($offset, $this->config);
     }
 
+    #[\ReturnTypeWillChange]
     public function offsetGet($offset)
     {
         return $this->get($offset);
     }
 
+    #[\ReturnTypeWillChange]
     public function offsetSet($offset, $value)
     {
         $this->set($offset, $value);
     }
 
+    #[\ReturnTypeWillChange]
     public function offsetUnset($offset)
     {
         $this->set($offset, null);
     }
 
+    #[\ReturnTypeWillChange]
     public function jsonSerialize()
     {
         return $this->config;