diff --git a/composer.lock b/composer.lock
index b26726364f..7d5e540e67 100644
--- a/composer.lock
+++ b/composer.lock
@@ -3329,6 +3329,12 @@
                 "url": "https://git.drupal.org/project/coder.git",
                 "reference": "984c54a7b1e8f27ff1c32348df69712afd86b17f"
             },
+            "dist": {
+                "type": "zip",
+                "url": "https://api.github.com/repos/klausi/coder/zipball/984c54a7b1e8f27ff1c32348df69712afd86b17f",
+                "reference": "984c54a7b1e8f27ff1c32348df69712afd86b17f",
+                "shasum": ""
+            },
             "require": {
                 "ext-mbstring": "*",
                 "php": ">=5.4.0",
diff --git a/core/lib/Drupal/Component/Scaffold/composer.json b/core/lib/Drupal/Component/Scaffold/composer.json
index 54b1ce8950..6f77bf7ad0 100644
--- a/core/lib/Drupal/Component/Scaffold/composer.json
+++ b/core/lib/Drupal/Component/Scaffold/composer.json
@@ -8,12 +8,18 @@
         "composer-plugin-api": "^1.0.0"
     },
     "require-dev": {
-        "composer/composer": "^1.8"
+        "composer/composer": "^1.8",
+        "symfony/process": "~3.4.0"
     },
     "autoload": {
-        "psr-4": {
-            "Drupal\\Component\\Scaffold\\": "src/"
-        }
+        "classmap": [
+            "CommandProvider.php",
+            "DrupalScaffoldCommand.php",
+            "FileFetcher.php",
+            "Handler.php",
+            "Plugin.php",
+            "PrestissimoFileFetcher.php"
+        ]
     },
     "extra": {
         "class": "Drupal\\Component\\Scaffold\\Plugin"
diff --git a/core/tests/Drupal/Tests/Component/Scaffold/PluginTest.php b/core/tests/Drupal/Tests/Component/Scaffold/PluginTest.php
index 9b43914bbc..92c4338edd 100644
--- a/core/tests/Drupal/Tests/Component/Scaffold/PluginTest.php
+++ b/core/tests/Drupal/Tests/Component/Scaffold/PluginTest.php
@@ -4,6 +4,7 @@
 
 use Composer\Util\Filesystem;
 use PHPUnit\Framework\TestCase;
+use Symfony\Component\Process\Process;
 
 /**
  * Tests composer plugin functionality.
@@ -83,7 +84,7 @@ public function testComposerInstallAndUpdate() {
     $this->assertFileExists($exampleScaffoldFile, 'Scaffold file should be automatically installed.');
 
     $this->fs->remove($exampleScaffoldFile);
-    $this->assertFileNotExists($exampleScaffoldFile, 'Scaffold file should not be exist.');
+    $this->assertFileNotExists($exampleScaffoldFile, 'Scaffold file should not exist.');
     $this->composer('drupal:scaffold');
     $this->assertFileExists($exampleScaffoldFile, 'Scaffold file should be installed by "drupal:scaffold" command.');
 
@@ -150,11 +151,12 @@ protected function composerJSONDefaults() {
    *   Composer command name, arguments and/or options.
    */
   protected function composer($command) {
-    chdir($this->tmpDir);
-    passthru(escapeshellcmd($this->drupalRootDir . '/vendor/bin/composer ' . $command), $exit_code);
-    if ($exit_code !== 0) {
-      throw new \Exception('Composer returned a non-zero exit code');
-    }
+    $commands = [
+      $this->drupalRootDir . '/vendor/bin/composer',
+      $command,
+    ];
+    $ps = new Process(implode(' ', $commands), $this->tmpDir);
+    $ps->mustRun();
   }
 
   /**