diff --git a/core/composer.json b/core/composer.json
index 0d103002c7..f34ac41899 100644
--- a/core/composer.json
+++ b/core/composer.json
@@ -45,6 +45,7 @@
         "jcalderonzumba/mink-phantomjs-driver": "^0.3.1",
         "mikey179/vfsStream": "^1.2",
         "phpunit/phpunit": ">=4.8.35 <5",
+        "phpspec/prophecy": "^1.4",
         "symfony/css-selector": "^3.2",
         "symfony/phpunit-bridge": "^3.2"
     },