diff --git a/src/Composer/Json/JsonFile.php b/src/Composer/Json/JsonFile.php
index 95ae95ea2..1b662fa91 100644
--- a/src/Composer/Json/JsonFile.php
+++ b/src/Composer/Json/JsonFile.php
@@ -180,15 +180,15 @@ class JsonFile
     {
         $content = file_get_contents($this->path);
         $data = json_decode($content);
-        $requiredSchemaData = array();
 
         if (null === $data && 'null' !== $content) {
             self::validateSyntax($content, $this->path);
         }
 
+        $isComposerSchemaFile = false;
         if (null === $schemaFile) {
+            $isComposerSchemaFile = true;
             $schemaFile = __DIR__ . self::COMPOSER_SCHEMA_PATH;
-            $requiredSchemaData = array('name', 'description');
         }
 
         // Prepend with file:// only when not using a special schema already (e.g. in the phar)
@@ -198,16 +198,17 @@ class JsonFile
 
         $schemaData = (object) array('$ref' => $schemaFile);
 
-        if ($schema !== self::LAX_SCHEMA) {
+        if ($schema === self::LAX_SCHEMA) {
+            $schemaData->additionalProperties = true;
+            $schemaData->required = array();
+        } elseif ($schema === self::STRICT_SCHEMA && $isComposerSchemaFile) {
             $schemaData->additionalProperties = false;
-            $schemaData->required = $requiredSchemaData;
+            $schemaData->required = array('name', 'description');
         }
 
         $validator = new Validator();
         $validator->check($data, $schemaData);
 
-        // TODO add more validation like check version constraints and such, perhaps build that into the arrayloader?
-
         if (!$validator->isValid()) {
             $errors = array();
             foreach ((array) $validator->getErrors() as $error) {