diff --git a/src/Composer/Repository/RepositoryManager.php b/src/Composer/Repository/RepositoryManager.php
index 05dcc1b4a..649c66cd9 100644
--- a/src/Composer/Repository/RepositoryManager.php
+++ b/src/Composer/Repository/RepositoryManager.php
@@ -89,6 +89,18 @@ class RepositoryManager
         $this->repositories[] = $repository;
     }
 
+    /**
+     * Adds a repository to the beginning of the chain
+     *
+     * This is useful when injecting additional repositories that should trump Packagist, e.g. from a plugin.
+     *
+     * @param RepositoryInterface $repository repository instance
+     */
+    public function prependRepository(RepositoryInterface $repository)
+    {
+        array_unshift($this->repositories, $repository);
+    }
+
     /**
      * Returns a new repository for a specific installation type.
      *