diff --git a/composer.json b/composer.json
index db85e2de..ed157386 100755
--- a/composer.json
+++ b/composer.json
@@ -19,7 +19,7 @@
         "psr/simple-cache": "^1.0 | ^2.0 | ^3.0",
         "psr/simple-cache-implementation": "^1.0 | ^2.0 | ^3.0",
         "lastguest/murmurhash": "^2.1",
-        "psr/http-message": "^1.0",
+        "psr/http-message": "^1.0 | ^2.0",
         "php-http/discovery": "^1.14"
     },
     "autoload": {
diff --git a/src/Helper/StringStream.php b/src/Helper/StringStream.php
index 22255b8a..e57a2fe9 100755
--- a/src/Helper/StringStream.php
+++ b/src/Helper/StringStream.php
@@ -32,7 +32,7 @@ public function __construct(
         rewind($this->stream);
     }
 
-    public function __toString()
+    public function __toString(): string
     {
         $stream = $this->stream;
         if ($stream === null) {