diff --git a/composer.json b/composer.json
index e5c783d..33deea0 100644
--- a/composer.json
+++ b/composer.json
@@ -28,7 +28,7 @@
         "php": ">=5.6",
         "phpunit/php-code-coverage": "~4.0||~5.0",
         "behat/behat": "~3.0",
-        "guzzlehttp/guzzle": "~4.0",
+        "guzzlehttp/guzzle": "~4.0||~5.0||~6.0",
         "symfony/config": "~2.3||~3.0",
         "symfony/dependency-injection": "~2.2||~3.0",
         "symfony/expression-language": "~2.2||~3.0",