diff --git a/composer.json b/composer.json
index e34c2cc3..2a96cda2 100644
--- a/composer.json
+++ b/composer.json
@@ -25,6 +25,7 @@
     },
     "require-dev": {
         "silverstripe/versioned": "^1@dev",
+        "sminnee/phpunit-mock-objects": "^3.4.5",
         "phpunit/phpunit": "^5.7"
     },
     "suggest": {