diff --git a/src/Composer/Package/Loader/JsonLoader.php b/src/Composer/Package/Loader/JsonLoader.php
index 27cc8ea77..27ff7c15a 100644
--- a/src/Composer/Package/Loader/JsonLoader.php
+++ b/src/Composer/Package/Loader/JsonLoader.php
@@ -23,6 +23,8 @@ class JsonLoader extends ArrayLoader
     {
         if ($json instanceof JsonFile) {
             $config = $json->read();
+        } elseif (file_exists($json)) {
+            $config = JsonFile::parseJson(file_get_contents($json));
         } elseif (is_string($json)) {
             $config = JsonFile::parseJson($json);
         }