diff --git a/res/composer-schema.json b/res/composer-schema.json
index d6e149c9d..96b708f88 100644
--- a/res/composer-schema.json
+++ b/res/composer-schema.json
@@ -2,8 +2,6 @@
     "$schema": "https://json-schema.org/draft-04/schema#",
     "title": "Package",
     "type": "object",
-    "additionalProperties": false,
-    "required": [ "name", "description" ],
     "properties": {
         "name": {
             "type": "string",
diff --git a/src/Composer/Json/JsonFile.php b/src/Composer/Json/JsonFile.php
index b15098d56..07a6f922f 100644
--- a/src/Composer/Json/JsonFile.php
+++ b/src/Composer/Json/JsonFile.php
@@ -196,9 +196,9 @@ class JsonFile
 
         $schemaData = (object) array('$ref' => $schemaFile);
 
-        if ($schema === self::LAX_SCHEMA) {
-            $schemaData->additionalProperties = true;
-            $schemaData->required = array();
+        if ($schema !== self::LAX_SCHEMA) {
+            $schemaData->additionalProperties = false;
+            $schemaData->required = array('name', 'description');
         }
 
         $validator = new Validator();
diff --git a/tests/Composer/Test/Json/ComposerSchemaTest.php b/tests/Composer/Test/Json/ComposerSchemaTest.php
index 0eece664c..5c53b2937 100644
--- a/tests/Composer/Test/Json/ComposerSchemaTest.php
+++ b/tests/Composer/Test/Json/ComposerSchemaTest.php
@@ -37,24 +37,6 @@ class ComposerSchemaTest extends TestCase
         $this->assertEquals($expectedError, $this->check($json));
     }
 
-    public function testRequiredProperties()
-    {
-        $json = '{ }';
-        $result = $this->check($json);
-        $this->assertContains(array('property' => 'name', 'message' => 'The property name is required', 'constraint' => 'required'), $result);
-        $this->assertContains(array('property' => 'description', 'message' => 'The property description is required', 'constraint' => 'required'), $result);
-
-        $json = '{ "name": "vendor/package" }';
-        $this->assertEquals(array(
-            array('property' => 'description', 'message' => 'The property description is required', 'constraint' => 'required'),
-        ), $this->check($json));
-
-        $json = '{ "description": "generic description" }';
-        $this->assertEquals(array(
-            array('property' => 'name', 'message' => 'The property name is required', 'constraint' => 'required'),
-        ), $this->check($json));
-    }
-
     public function testOptionalAbandonedProperty()
     {
         $json = '{"name": "vendor/package", "description": "description", "abandoned": true}';
diff --git a/tests/Composer/Test/Json/JsonFileTest.php b/tests/Composer/Test/Json/JsonFileTest.php
index 8f8b6a2c2..3a19b2fe7 100644
--- a/tests/Composer/Test/Json/JsonFileTest.php
+++ b/tests/Composer/Test/Json/JsonFileTest.php
@@ -14,6 +14,7 @@ namespace Composer\Test\Json;
 
 use Seld\JsonLint\ParsingException;
 use Composer\Json\JsonFile;
+use Composer\Json\JsonValidationException;
 use Composer\Test\TestCase;
 
 class JsonFileTest extends TestCase
@@ -93,6 +94,89 @@ class JsonFileTest extends TestCase
     {
         $json = new JsonFile(__DIR__.'/Fixtures/composer.json');
         $this->assertTrue($json->validateSchema());
+        $this->assertTrue($json->validateSchema(JsonFile::LAX_SCHEMA));
+    }
+
+    public function testSchemaValidationError()
+    {
+        $file = tempnam(sys_get_temp_dir(), 'c');
+        file_put_contents($file, '{ "name": null }');
+        $json = new JsonFile($file);
+        $expectedMessage = sprintf('"%s" does not match the expected JSON schema', $file);
+        $expectedError = 'name : NULL value found, but a string is required';
+        try {
+            $json->validateSchema();
+            $this->fail('Expected exception to be thrown (strict)');
+        } catch (JsonValidationException $e) {
+            $this->assertEquals($expectedMessage, $e->getMessage());
+            $this->assertContains($expectedError, $e->getErrors());
+        }
+        try {
+            $json->validateSchema(JsonFile::LAX_SCHEMA);
+            $this->fail('Expected exception to be thrown (lax)');
+        } catch (JsonValidationException $e) {
+            $this->assertEquals($expectedMessage, $e->getMessage());
+            $this->assertContains($expectedError, $e->getErrors());
+        }
+        unlink($file);
+    }
+
+    public function testSchemaValidationLaxAdditionalProperties()
+    {
+        $file = tempnam(sys_get_temp_dir(), 'c');
+        file_put_contents($file, '{ "name": "vendor/package", "description": "generic description", "foo": "bar" }');
+        $json = new JsonFile($file);
+        try {
+            $json->validateSchema();
+            $this->fail('Expected exception to be thrown (strict)');
+        } catch (JsonValidationException $e) {
+            $this->assertEquals(sprintf('"%s" does not match the expected JSON schema', $file), $e->getMessage());
+            $this->assertEquals(array('The property foo is not defined and the definition does not allow additional properties'), $e->getErrors());
+        }
+        $this->assertTrue($json->validateSchema(JsonFile::LAX_SCHEMA));
+        unlink($file);
+    }
+
+    public function testSchemaValidationLaxRequired()
+    {
+        $file = tempnam(sys_get_temp_dir(), 'c');
+        $json = new JsonFile($file);
+
+        $expectedMessage = sprintf('"%s" does not match the expected JSON schema', $file);
+
+        file_put_contents($file, '{ }');
+        try {
+            $json->validateSchema();
+            $this->fail('Expected exception to be thrown (strict)');
+        } catch (JsonValidationException $e) {
+            $this->assertEquals($expectedMessage, $e->getMessage());
+            $errors = $e->getErrors();
+            $this->assertContains('name : The property name is required', $errors);
+            $this->assertContains('description : The property description is required', $errors);
+        }
+        $this->assertTrue($json->validateSchema(JsonFile::LAX_SCHEMA));
+
+        file_put_contents($file, '{ "name": "vendor/package" }');
+        try {
+            $json->validateSchema();
+            $this->fail('Expected exception to be thrown (strict)');
+        } catch (JsonValidationException $e) {
+            $this->assertEquals($expectedMessage, $e->getMessage());
+            $this->assertEquals(array('description : The property description is required'), $e->getErrors());
+        }
+        $this->assertTrue($json->validateSchema(JsonFile::LAX_SCHEMA));
+
+        file_put_contents($file, '{ "description": "generic description" }');
+        try {
+            $json->validateSchema();
+            $this->fail('Expected exception to be thrown (strict)');
+        } catch (JsonValidationException $e) {
+            $this->assertEquals($expectedMessage, $e->getMessage());
+            $this->assertEquals(array('name : The property name is required'), $e->getErrors());
+        }
+        $this->assertTrue($json->validateSchema(JsonFile::LAX_SCHEMA));
+
+        unlink($file);
     }
 
     public function testParseErrorDetectMissingCommaMultiline()