diff --git a/composer.json b/composer.json
index 505382e..ae1717a 100644
--- a/composer.json
+++ b/composer.json
@@ -23,6 +23,6 @@
         "php": ">=5.2.0"
     },
     "require-dev": {
-        "phpunit/phpunit": "~6.0"
+        "phpunit/phpunit": "~5.7 || ~6.0"
     }
 }
\ No newline at end of file
diff --git a/composer.lock b/composer.lock
index 508fc28..8c2acb3 100644
--- a/composer.lock
+++ b/composer.lock
@@ -4,7 +4,7 @@
         "Read more about it at https://getcomposer.org/doc/01-basic-usage.md#composer-lock-the-lock-file",
         "This file is @generated automatically"
     ],
-    "content-hash": "7f142647ccc78d906bfcd06d760b28de",
+    "content-hash": "85da402be27c9e73232ed9bfa7a7c83c",
     "packages": [],
     "packages-dev": [
         {