diff --git a/src/Symfony/Installer/DemoCommand.php b/src/Symfony/Installer/DemoCommand.php
index ffe1ff7..16970fb 100644
--- a/src/Symfony/Installer/DemoCommand.php
+++ b/src/Symfony/Installer/DemoCommand.php
@@ -75,6 +75,7 @@ protected function execute(InputInterface $input, OutputInterface $output)
                 ->download()
                 ->extract()
                 ->cleanUp()
+                ->updateComposerJson()
                 ->createGitIgnore()
                 ->checkSymfonyRequirements()
                 ->displayInstallationResult()
diff --git a/src/Symfony/Installer/DownloadCommand.php b/src/Symfony/Installer/DownloadCommand.php
index 5d9b28e..aa8ef17 100644
--- a/src/Symfony/Installer/DownloadCommand.php
+++ b/src/Symfony/Installer/DownloadCommand.php
@@ -325,6 +325,33 @@ protected function checkSymfonyRequirements()
         return $this;
     }
 
+    /**
+     * Updates the composer.json file to provide better values for some of the
+     * default configuration values.
+     *
+     * @return $this
+     */
+    protected function updateComposerJson()
+    {
+        $composerConfig = $this->getProjectComposerConfig();
+
+        if (isset($composerConfig['config']['platform']['php'])) {
+            unset($composerConfig['config']['platform']['php']);
+
+            if (empty($composerConfig['config']['platform'])) {
+                unset($composerConfig['config']['platform']);
+            }
+
+            if (empty($composerConfig['config'])) {
+                unset($composerConfig['config']);
+            }
+        }
+
+        $this->saveProjectComposerConfig($composerConfig);
+
+        return $this;
+    }
+
     /**
      * Creates the appropriate .gitignore file for a Symfony project if it doesn't exist.
      *
@@ -544,6 +571,107 @@ protected function getUrlContents($url)
         return $client->get($url)->getBody()->getContents();
     }
 
+    /**
+     * It returns the project's Composer config as a PHP array.
+     *
+     * @return $this|array
+     */
+    protected function getProjectComposerConfig()
+    {
+        $composerJsonFilepath = $this->projectDir.'/composer.json';
+
+        if (!is_writable($composerJsonFilepath)) {
+            if ($this->output->isVerbose()) {
+                $this->output->writeln(sprintf(
+                    " <comment>[WARNING]</comment> Project's Composer config cannot be updated because\n".
+                    " the <comment>%s</comment> file is not writable.\n",
+                    $composerJsonFilepath
+                ));
+            }
+
+            return $this;
+        }
+
+        return json_decode(file_get_contents($composerJsonFilepath), true);
+    }
+
+    /**
+     * It saves the given PHP array as the project's Composer config. In addition
+     * to JSON-serializing the contents, it synchronizes the composer.lock file to
+     * avoid out-of-sync Composer errors.
+     *
+     * @param array $config
+     */
+    protected function saveProjectComposerConfig(array $config)
+    {
+        $composerJsonFilepath = $this->projectDir.'/composer.json';
+        $this->fs->dumpFile($composerJsonFilepath, json_encode($config, JSON_PRETTY_PRINT | JSON_UNESCAPED_SLASHES)."\n");
+
+        $this->syncComposerLockFile();
+    }
+
+    /**
+     * Updates the hash values stored in composer.lock to avoid out-of-sync
+     * problems when the composer.json file contents are changed.
+     */
+    private function syncComposerLockFile()
+    {
+        $composerJsonFileContents = file_get_contents($this->projectDir.'/composer.json');
+        $composerLockFileContents = json_decode(file_get_contents($this->projectDir.'/composer.lock'), true);
+
+        if (array_key_exists('hash', $composerLockFileContents)) {
+            $composerLockFileContents['hash'] = md5($composerJsonFileContents);
+        }
+
+        if (array_key_exists('content-hash', $composerLockFileContents)) {
+            $composerLockFileContents['content-hash'] = $this->getComposerContentHash($composerJsonFileContents);
+        }
+
+        $this->fs->dumpFile($this->projectDir.'/composer.lock', json_encode($composerLockFileContents, JSON_PRETTY_PRINT | JSON_UNESCAPED_SLASHES)."\n");
+    }
+
+    /**
+     * Returns the md5 hash of the sorted content of the composer file.
+     *
+     * @see https://github.com/composer/composer/blob/master/src/Composer/Package/Locker.php (getContentHash() method)
+     *
+     * @param string $composerJsonFileContents The contents of the composer.json file.
+     *
+     * @return string The hash of the composer file content.
+     */
+    private function getComposerContentHash($composerJsonFileContents)
+    {
+        $composerConfig = json_decode($composerJsonFileContents, true);
+
+        $relevantKeys = array(
+            'name',
+            'version',
+            'require',
+            'require-dev',
+            'conflict',
+            'replace',
+            'provide',
+            'minimum-stability',
+            'prefer-stable',
+            'repositories',
+            'extra',
+        );
+
+        $relevantComposerConfig = array();
+
+        foreach (array_intersect($relevantKeys, array_keys($composerConfig)) as $key) {
+            $relevantComposerConfig[$key] = $composerConfig[$key];
+        }
+
+        if (isset($composerConfig['config']['platform'])) {
+            $relevantComposerConfig['config']['platform'] = $composerConfig['config']['platform'];
+        }
+
+        ksort($relevantComposerConfig);
+
+        return md5(json_encode($relevantComposerConfig));
+    }
+
     /**
      * Enables the signal handler.
      *
diff --git a/src/Symfony/Installer/NewCommand.php b/src/Symfony/Installer/NewCommand.php
index 41f477a..048c4aa 100644
--- a/src/Symfony/Installer/NewCommand.php
+++ b/src/Symfony/Installer/NewCommand.php
@@ -337,48 +337,22 @@ protected function updateParameters()
      */
     protected function updateComposerJson()
     {
-        $filename = $this->projectDir.'/composer.json';
+        parent::updateComposerJson();
 
-        if (!is_writable($filename)) {
-            if ($this->output->isVerbose()) {
-                $this->output->writeln(sprintf(
-                    " <comment>[WARNING]</comment> Project name cannot be configured because\n".
-                    " the <comment>%s</comment> file is not writable.\n",
-                    $filename
-                ));
-            }
-
-            return $this;
-        }
-
-        $contents = json_decode(file_get_contents($filename), true);
+        $composerConfig = $this->getProjectComposerConfig();
 
-        $contents['name'] = $this->generateComposerProjectName();
-        $contents['license'] = 'proprietary';
+        $composerConfig['name'] = $this->generateComposerProjectName();
+        $composerConfig['license'] = 'proprietary';
 
-        if (isset($contents['description'])) {
-            unset($contents['description']);
+        if (isset($composerConfig['description'])) {
+            unset($composerConfig['description']);
         }
 
-        if (isset($contents['config']['platform']['php'])) {
-            unset($contents['config']['platform']['php']);
-
-            if (empty($contents['config']['platform'])) {
-                unset($contents['config']['platform']);
-            }
-
-            if (empty($contents['config'])) {
-                unset($contents['config']);
-            }
-        }
-
-        if (isset($contents['extra']['branch-alias'])) {
-            unset($contents['extra']['branch-alias']);
+        if (isset($composerConfig['extra']['branch-alias'])) {
+            unset($composerConfig['extra']['branch-alias']);
         }
 
-        file_put_contents($filename, json_encode($contents, JSON_PRETTY_PRINT | JSON_UNESCAPED_SLASHES)."\n");
-
-        $this->syncComposerLockFile();
+        $this->saveProjectComposerConfig($composerConfig);
 
         return $this;
     }
@@ -441,66 +415,4 @@ protected function getRemoteFileUrl()
     {
         return 'http://symfony.com/download?v=Symfony_Standard_Vendors_'.$this->version;
     }
-
-    /**
-     * Updates the hash values stored in composer.lock to avoid out-of-sync
-     * problems when the composer.json file contents are changed.
-     */
-    private function syncComposerLockFile()
-    {
-        $composerJsonFileContents = file_get_contents($this->projectDir.'/composer.json');
-        $composerLockFileContents = json_decode(file_get_contents($this->projectDir.'/composer.lock'), true);
-
-        if (array_key_exists('hash', $composerLockFileContents)) {
-            $composerLockFileContents['hash'] = md5($composerJsonFileContents);
-        }
-
-        if (array_key_exists('content-hash', $composerLockFileContents)) {
-            $composerLockFileContents['content-hash'] = $this->getComposerContentHash($composerJsonFileContents);
-        }
-
-        file_put_contents($this->projectDir.'/composer.lock', json_encode($composerLockFileContents, JSON_PRETTY_PRINT | JSON_UNESCAPED_SLASHES)."\n");
-    }
-
-    /**
-     * Returns the md5 hash of the sorted content of the composer file.
-     *
-     * @see https://github.com/composer/composer/blob/master/src/Composer/Package/Locker.php (getContentHash() method)
-     *
-     * @param string $composerJsonFileContents The contents of the composer.json file.
-     *
-     * @return string The hash of the composer file content.
-     */
-    private function getComposerContentHash($composerJsonFileContents)
-    {
-        $content = json_decode($composerJsonFileContents, true);
-
-        $relevantKeys = array(
-            'name',
-            'version',
-            'require',
-            'require-dev',
-            'conflict',
-            'replace',
-            'provide',
-            'minimum-stability',
-            'prefer-stable',
-            'repositories',
-            'extra',
-        );
-
-        $relevantContent = array();
-
-        foreach (array_intersect($relevantKeys, array_keys($content)) as $key) {
-            $relevantContent[$key] = $content[$key];
-        }
-
-        if (isset($content['config']['platform'])) {
-            $relevantContent['config']['platform'] = $content['config']['platform'];
-        }
-
-        ksort($relevantContent);
-
-        return md5(json_encode($relevantContent));
-    }
 }
diff --git a/tests/Symfony/Installer/Tests/IntegrationTest.php b/tests/Symfony/Installer/Tests/IntegrationTest.php
index fb300d3..4dd252d 100644
--- a/tests/Symfony/Installer/Tests/IntegrationTest.php
+++ b/tests/Symfony/Installer/Tests/IntegrationTest.php
@@ -50,6 +50,10 @@ public function testDemoApplicationInstallation()
 
         $output = $this->runCommand('php app/console --version', $projectDir);
         $this->assertRegExp('/Symfony version 2\.\d+\.\d+(-DEV)? - app\/dev\/debug/', $output);
+
+        $composerConfig = json_decode(file_get_contents($projectDir.'/composer.json'), true);
+
+        $this->assertArrayNotHasKey('platform', $composerConfig['config'], 'The composer.json file does not define any platform configuration.');
     }
 
     /**
@@ -75,6 +79,13 @@ public function testSymfonyInstallation($versionToInstall, $messageRegexp, $vers
         }
 
         $this->assertRegExp($versionRegexp, $output);
+
+        $composerConfig = json_decode(file_get_contents($projectDir.'/composer.json'), true);
+        $this->assertArrayNotHasKey(
+            isset($composerConfig['config']) ? 'platform' : 'config',
+            isset($composerConfig['config']) ? $composerConfig['config'] : $composerConfig,
+            'The composer.json file does not define any platform configuration.'
+        );
     }
 
     public function testSymfonyInstallationInCurrentDirectory()