diff --git a/core/lib/Drupal/Core/Composer/ExtensionDependencyChecker.php b/core/lib/Drupal/Core/Composer/ExtensionDependencyChecker.php
index 3ac601d..f801ccc 100644
--- a/core/lib/Drupal/Core/Composer/ExtensionDependencyChecker.php
+++ b/core/lib/Drupal/Core/Composer/ExtensionDependencyChecker.php
@@ -99,7 +99,7 @@ public function getUnmetDependencies(Extension $extension) {
       if (strpos($package_name, '/') === FALSE) {
         continue;
       }
-      // Rule out extension dependencies specified in the info.yml file.
+      // Skip extension dependencies specified in the info.yml file.
       if (strpos($package_name, 'drupal/') === 0) {
         if (in_array(substr($package_name, 7), $info_dependencies)) {
           continue;
diff --git a/core/modules/system/src/Tests/Module/HookRequirementsTest.php b/core/modules/system/src/Tests/Module/HookRequirementsTest.php
index 760e423..632be0c 100644
--- a/core/modules/system/src/Tests/Module/HookRequirementsTest.php
+++ b/core/modules/system/src/Tests/Module/HookRequirementsTest.php
@@ -27,48 +27,79 @@ function testHookRequirementsFailure() {
   }
 
   /**
-   * Tests that a module with uninstalled dependencies is not installable.
+   * Tests that modules with uninstalled dependencies are not installable.
    */
   public function testComposerDependenciesFailure() {
-    $this->assertModules(['composer_uninstallable'], FALSE);
+    $data = [
+      [
+        'composer_uninstallable',
+        'The following extensions have unmet Composer-based dependencies: composer_uninstallable (scalopus/empty: ^1.1, jellyfish/empty: ~2.0, ordinal/empty: 4.0.*). Read the documentation on drupal.org on how to install them.',
+      ],
+      [
+        'composer_mixed_uninstallable',
+        'The following extensions have unmet Composer-based dependencies: composer_mixed_uninstallable (drupal/system: ^8.2). Read the documentation on drupal.org on how to install them.',
+      ],
+    ];
+    foreach ($data as $datum) {
+      $this->assertComposerDependenciesFailure($datum[0], $datum[1]);
+    }
+  }
+
+  /**
+   * Tests that a module with uninstalled dependencies is not installable.
+   */
+  public function assertComposerDependenciesFailure($module, $error_message) {
+    $this->assertModules([$module], FALSE);
 
-    // Attempt to install the composer_uninstallable module using internals.
-    // This should throw a
+    // Attempt to install the module using internals. This should throw a
     // \Drupal\Core\Extension\ExtensionComposerRequirementsException.
-    $message = sprintf('Attempting to install composer_uninstallable threw %s.', ExtensionComposerRequirementsException::class);
+    $message = sprintf('Attempting to install %s threw %s.', $module, ExtensionComposerRequirementsException::class);
     try {
       $installer = $this->container->get('module_installer');
-      $installer->install(['composer_uninstallable'], TRUE);
+      $installer->install([$module], TRUE);
       $this->fail($message);
     }
     catch (ExtensionComposerRequirementsException $e) {
       $this->pass($message);
     }
 
-    // Attempt to install the composer_uninstallable module using the module
-    // list form. This should fail with a message to the user.
+    // Attempt to install the $module module using the module list form. This
+    // should fail with a message to the user.
     $edit = [];
-    $edit['modules[Testing][composer_uninstallable][enable]'] = 'composer_uninstallable';
+    $edit["modules[Testing][$module][enable]"] = '$module';
     $this->drupalPostForm('admin/modules', $edit, t('Install'));
 
-    $this->assertText('The following extensions have unmet Composer-based dependencies: composer_uninstallable (scalopus/empty: ^1.1, jellyfish/empty: ~2.0, ordinal/empty: 4.0.*). Read the documentation on drupal.org on how to install them.');
+    $this->assertText($error_message);
     // Makes sure the module was NOT installed.
-    $this->assertModules(['composer_uninstallable'], FALSE);
+    $this->assertModules([$module], FALSE);
   }
 
   /**
-   * Tests that a module with installed dependencies is installable.
+   * Tests that modules with installed dependencies are installable.
    */
   public function testComposerDependenciesSuccess() {
-    $this->assertModules(['composer_installable'], FALSE);
+    $data = [
+      'composer_installable',
+      'composer_mixed_installable',
+    ];
+    foreach ($data as $datum) {
+      $this->assertComposerDependenciesSuccess($datum);
+    }
+  }
+
+  /**
+   * Tests that modules with installed dependencies are installable.
+   */
+  public function assertComposerDependenciesSuccess($module) {
+    $this->assertModules([$module], FALSE);
 
-    // Attempt to install the composer_installable module.
+    // Attempt to install the module.
     $edit = [];
-    $edit['modules[Testing][composer_installable][enable]'] = 'composer_installable';
+    $edit["modules[Testing][$module][enable]"] = $module;
     $this->drupalPostForm('admin/modules', $edit, t('Install'));
 
     // Makes sure the module was installed.
-    $this->assertModules(['composer_installable'], TRUE);
+    $this->assertModules([$module], TRUE);
   }
 
 }
diff --git a/core/modules/system/tests/modules/composer_mixed_installable/composer.json b/core/modules/system/tests/modules/composer_mixed_installable/composer.json
new file mode 100644
index 0000000..4f0d5a7
--- /dev/null
+++ b/core/modules/system/tests/modules/composer_mixed_installable/composer.json
@@ -0,0 +1,7 @@
+{
+  "name": "drupal_test/composer_mixed_installable",
+  "description": "Test module that is installable because it declares a core dependency in both composer.json and info.yml.",
+  "require": {
+    "drupal/system": "^8.2"
+  }
+}
diff --git a/core/modules/system/tests/modules/composer_mixed_installable/composer_mixed_installable.info.yml b/core/modules/system/tests/modules/composer_mixed_installable/composer_mixed_installable.info.yml
new file mode 100644
index 0000000..c4fded8
--- /dev/null
+++ b/core/modules/system/tests/modules/composer_mixed_installable/composer_mixed_installable.info.yml
@@ -0,0 +1,8 @@
+name: 'Composer Mixed Installable'
+type: module
+description: 'Test module that is installable because it declares a core dependency in both composer.json and info.yml.'
+package: Testing
+version: VERSION
+core: 8.x
+dependencies:
+  - system
diff --git a/core/modules/system/tests/modules/composer_mixed_uninstallable/composer.json b/core/modules/system/tests/modules/composer_mixed_uninstallable/composer.json
new file mode 100644
index 0000000..e79cab5
--- /dev/null
+++ b/core/modules/system/tests/modules/composer_mixed_uninstallable/composer.json
@@ -0,0 +1,7 @@
+{
+  "name": "drupal_test/composer_mixed_uninstallable",
+  "description": "Test module that is not installable because it declares a core dependency in composer.json but not info.yml.",
+  "require": {
+    "drupal/system": "^8.2"
+  }
+}
diff --git a/core/modules/system/tests/modules/composer_mixed_uninstallable/composer_mixed_uninstallable.info.yml b/core/modules/system/tests/modules/composer_mixed_uninstallable/composer_mixed_uninstallable.info.yml
new file mode 100644
index 0000000..21007ed
--- /dev/null
+++ b/core/modules/system/tests/modules/composer_mixed_uninstallable/composer_mixed_uninstallable.info.yml
@@ -0,0 +1,6 @@
+name: 'Composer Mixed Uninstallable'
+type: module
+description: 'Test module that is not installable because it declares a core dependency in composer.json but not info.yml.'
+package: Testing
+version: VERSION
+core: 8.x
diff --git a/core/tests/Drupal/Tests/Core/Composer/ExtensionDependencyCheckerTest.php b/core/tests/Drupal/Tests/Core/Composer/ExtensionDependencyCheckerTest.php
index b5c80fc..9d4384e 100644
--- a/core/tests/Drupal/Tests/Core/Composer/ExtensionDependencyCheckerTest.php
+++ b/core/tests/Drupal/Tests/Core/Composer/ExtensionDependencyCheckerTest.php
@@ -143,6 +143,7 @@ public function testDependenciesAreMet($expected, $composer_json, $installed_jso
     $counter = static::$counter;
     $module_name = "some_module$counter";
 
+    // Make an info.yml file.
     $info = [
       'type' => 'module',
       'core' => '8.x',
@@ -151,8 +152,9 @@ public function testDependenciesAreMet($expected, $composer_json, $installed_jso
     if ($info_dependencies) {
       $info['dependencies'] = $info_dependencies;
     }
+    // Make a file system.
     $structure = [
-      'modules' => [$module_name => ["$module_name.info.yml" => Yaml::dump($info, 2, 2)]],
+      'modules' => [$module_name => ["$module_name.info.yml" => Yaml::dump($info)]],
       'vendor' => ['composer' => []],
     ];
     if ($installed_json !== NULL) {