diff --git a/src/ResponseBuilder.php b/src/ResponseBuilder.php
index e72c196..8d8d108 100644
--- a/src/ResponseBuilder.php
+++ b/src/ResponseBuilder.php
@@ -26,14 +26,14 @@ public function __construct(MockBuilder $mockBuilder)
         $this->response = new Response();
     }
 
-    public function statusCode($statusCode) : self
+    public function statusCode(int $statusCode) : self
     {
         $this->response = $this->response->withStatus($statusCode);
 
         return $this;
     }
 
-    public function body($body)
+    public function body(string $body) : self
     {
         $this->response = $this->response->withBody(stream_for($body));
 
@@ -47,7 +47,7 @@ public function callback(Closure $callback) : self
         return $this;
     }
 
-    public function header($header, $value) : self
+    public function header(string $header, string $value) : self
     {
         $this->response = $this->response->withHeader($header, $value);