diff --git a/composer.json b/composer.json
index ff25532..5f9c946 100644
--- a/composer.json
+++ b/composer.json
@@ -22,7 +22,7 @@
     "require": {
         "php": ">=5.4.0",
         "99designs/http-signatures": "~1.1",
-        "guzzlehttp/guzzle": "~4.2"
+        "guzzlehttp/guzzle": ">=4.2.0 <5.3.0"
     },
     "require-dev": {
         "phpunit/phpunit": "~4.1"