diff --git a/core/tests/Drupal/Tests/Composer/Plugin/Scaffold/Functional/ComposerHookTest.php b/core/tests/Drupal/Tests/Composer/Plugin/Scaffold/Functional/ComposerHookTest.php
index 9c755941da..49f2639c32 100644
--- a/core/tests/Drupal/Tests/Composer/Plugin/Scaffold/Functional/ComposerHookTest.php
+++ b/core/tests/Drupal/Tests/Composer/Plugin/Scaffold/Functional/ComposerHookTest.php
@@ -115,6 +115,15 @@ public function testComposerHooks() {
     $this->assertDirectoryExists($sut);
     $this->assertStringContainsString('Scaffolding files for fixtures/drupal-drupal', $stdout);
     $this->assertScaffoldedFile($sut . '/index.php', FALSE, 'Test version of index.php from drupal/core');
+    $topLevelProjectDir = 'composer-hooks-nothing-allowed-fixture';
+    $sut = $this->fixturesDir . '/' . $topLevelProjectDir;
+    // Run composer install on an empty project.
+    $this->mustExec("composer install --no-ansi", $sut);
+    // Require a project that is not allowed to scaffold and confirm that we
+    // get a warning, and it does not scaffold.
+    $this->executeCommand("composer require --no-ansi --no-interaction fixtures/drupal-assets-fixture:dev-main fixtures/scaffold-override-fixture:dev-main", $sut);
+    $this->assertCommandSuccessful();
+    $this->assertFileDoesNotExist($sut . '/sites/default/default.settings.php');
   }
 
   /**
diff --git a/core/tests/Drupal/Tests/Composer/Plugin/Scaffold/fixtures/composer-hooks-nothing-allowed-fixture/assets/robots-default.txt b/core/tests/Drupal/Tests/Composer/Plugin/Scaffold/fixtures/composer-hooks-nothing-allowed-fixture/assets/robots-default.txt
new file mode 100644
index 0000000000..a26bf8912f
--- /dev/null
+++ b/core/tests/Drupal/Tests/Composer/Plugin/Scaffold/fixtures/composer-hooks-nothing-allowed-fixture/assets/robots-default.txt
@@ -0,0 +1 @@
+# robots.txt fixture scaffolded from "file-mappings" in composer-hooks-fixture composer.json fixture.
diff --git a/core/tests/Drupal/Tests/Composer/Plugin/Scaffold/fixtures/composer-hooks-nothing-allowed-fixture/composer.json.tmpl b/core/tests/Drupal/Tests/Composer/Plugin/Scaffold/fixtures/composer-hooks-nothing-allowed-fixture/composer.json.tmpl
new file mode 100644
index 0000000000..b90299e625
--- /dev/null
+++ b/core/tests/Drupal/Tests/Composer/Plugin/Scaffold/fixtures/composer-hooks-nothing-allowed-fixture/composer.json.tmpl
@@ -0,0 +1,69 @@
+{
+  "name": "fixtures/drupal-drupal",
+  "type": "project",
+  "minimum-stability": "dev",
+  "prefer-stable": true,
+  "repositories": {
+    "packagist.org": false,
+    "composer-scaffold": {
+      "type": "path",
+      "url": "__PROJECT_ROOT__",
+      "options": {
+        "symlink": true
+      }
+    },
+    "drupal-core-fixture": {
+      "type": "path",
+      "url": "../drupal-core-fixture",
+      "options": {
+        "symlink": true
+      }
+    },
+    "drupal-assets-fixture": {
+      "type": "path",
+      "url": "../drupal-assets-fixture",
+      "options": {
+        "symlink": true
+      }
+    },
+    "scaffold-override-fixture": {
+      "type": "path",
+      "url": "../scaffold-override-fixture",
+      "options": {
+        "symlink": true
+      }
+    }
+  },
+  "require": {
+    "drupal/core-composer-scaffold": "*",
+    "fixtures/drupal-core-fixture": "*"
+  },
+  "extra": {
+    "drupal-scaffold": {
+      "locations": {
+        "web-root": "./"
+      },
+      "symlink": __SYMLINK__,
+      "file-mapping": {
+        "[web-root]/.htaccess": false,
+        "[web-root]/robots.txt": "assets/robots-default.txt"
+      }
+    },
+    "installer-paths": {
+      "core": ["type:drupal-core"],
+      "modules/contrib/{$name}": ["type:drupal-module"],
+      "modules/custom/{$name}": ["type:drupal-custom-module"],
+      "profiles/contrib/{$name}": ["type:drupal-profile"],
+      "profiles/custom/{$name}": ["type:drupal-custom-profile"],
+      "themes/contrib/{$name}": ["type:drupal-theme"],
+      "themes/custom/{$name}": ["type:drupal-custom-theme"],
+      "libraries/{$name}": ["type:drupal-library"],
+      "drush/Commands/contrib/{$name}": ["type:drupal-drush"]
+    }
+  },
+  "config": {
+     "allow-plugins": {
+       "drupal/core-composer-scaffold": false
+     }
+  }
+}