diff --git a/composer.json b/composer.json
index 0bd8e2e..7e14447 100644
--- a/composer.json
+++ b/composer.json
@@ -20,7 +20,7 @@
     },
     "require-dev": {
         "ext-json": "*",
-        "phpunit/phpunit": "^4.8",
+        "phpunit/phpunit": "^4.8.35",
         "ely/php-code-style": "^0.3.0"
     },
     "autoload": {
diff --git a/composer.lock b/composer.lock
index cf0f024..87600a1 100644
--- a/composer.lock
+++ b/composer.lock
@@ -4,7 +4,7 @@
         "Read more about it at https://getcomposer.org/doc/01-basic-usage.md#installing-dependencies",
         "This file is @generated automatically"
     ],
-    "content-hash": "715eede1be710927dc2f798522c84021",
+    "content-hash": "6fecc5deac2e564a7d0cb464b4c0fbe5",
     "packages": [
         {
             "name": "guzzlehttp/guzzle",