diff --git a/.travis.yml b/.travis.yml
index 5a4f48c..fb8310c 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -6,6 +6,11 @@ php:
   - 5.4
   - hhvm
 
-install: composer install
+install: composer require --no-update guzzlehttp/guzzle $GUZZLE_VERSION; composer update
 
 script: vendor/bin/phpunit
+
+env:
+  - GUZZLE_VERSION: 4.2
+  - GUZZLE_VERSION: 5.0
+  - GUZZLE_VERSION: 5.2
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"