diff --git a/core/lib/Drupal/Core/Asset/LibraryDiscoveryParser.php b/core/lib/Drupal/Core/Asset/LibraryDiscoveryParser.php
index e2c5250..47e6c2c 100644
--- a/core/lib/Drupal/Core/Asset/LibraryDiscoveryParser.php
+++ b/core/lib/Drupal/Core/Asset/LibraryDiscoveryParser.php
@@ -7,6 +7,7 @@
 
 namespace Drupal\Core\Asset;
 
+use Drupal\Component\Utility\SafeMarkup;
 use Drupal\Core\Asset\Exception\IncompleteLibraryDefinitionException;
 use Drupal\Core\Asset\Exception\InvalidLibraryFileException;
 use Drupal\Core\Asset\Exception\LibraryDefinitionMissingLicenseException;
@@ -87,7 +88,8 @@ public function buildByExtension($extension) {
       $path = $this->drupalGetPath($extension_type, $extension);
     }
 
-    $libraries = $this->applyLibrariesOverrides($this->parseLibraryInfo($extension, $path), $extension);
+    $libraries = $this->parseLibraryInfo($extension, $path);
+    $libraries = $this->applyLibrariesOverrides($libraries, $extension);
 
     foreach ($libraries as $id => &$library) {
       if (!isset($library['js']) && !isset($library['css']) && !isset($library['drupalSettings'])) {
@@ -330,11 +332,12 @@ protected function applyLibrariesOverrides($libraries, $extension) {
     $theme_path = $active_theme->getPath();
     foreach ($libraries as $name => $library) {
       // Process libraries overrides.
-      foreach ($libraries_overrides as $item => $override) {
+      foreach ($libraries_overrides as $asset => $override) {
         // Active theme defines an override for this library.
-        if ($item === "$extension/$name") {
-          // The whole library. Use the override key to specify that this
-          // library will be overridden when it is called.
+        if ($asset === "$extension/$name") {
+          // Active theme defines an override for the whole library. Use the
+          // override key to specify that this library will be overridden when
+          // it is called.
           // @see \Drupal\Core\Asset\LibraryDiscovery::getLibraryByName()
           if ($override) {
             $libraries[$name]['override'] = $override;
@@ -343,20 +346,28 @@ protected function applyLibrariesOverrides($libraries, $extension) {
             $libraries[$name]['override'] = FALSE;
           }
         }
-        else if (strpos($item, "$extension/$name/") !== FALSE) {
-          // An asset within the library.
-          list(, , $component, $value) = explode('/', $item, 4);
-          if ($component == 'css') {
-            // SMACSS-category should be incorporated into the component name.
+        else if (strpos($asset, "$extension/$name/") !== FALSE) {
+          // Active theme defines an override for an asset within this library.
+          // Throw an exception if the asset is not properly specified.
+          if (substr_count($asset, '/') < 3) {
+            throw new \LogicException(SafeMarkup::format('Library asset %asset is not correctly specified.', ['%asset' => $asset]));
+          }
+          list(, , $sub_key, $value) = explode('/', $asset, 4);
+          if ($sub_key === 'drupalSettings') {
+            // drupalSettings should not be overridden.
+            throw new \LogicException(SafeMarkup::format('drupalSettings cannot be overridden in libraries-override. Trying to override %asset.', ['%asset' =>$asset]));
+          }
+          else if ($sub_key === 'css') {
+            // SMACSS category should be incorporated into the asset name.
             list($category, $value) = explode('/', $value, 2);
-            $parents = [$component, $category, $value];
-            $new_parents = [$component, $category, '/' . $theme_path . '/' . $override];
+            $parents = [$sub_key, $category, $value];
+            $new_parents = [$sub_key, $category, '/' . $theme_path . '/' . $override];
           }
           else {
-            $parents = [$component, $value];
-            $new_parents = [$component, '/' . $theme_path . '/' . $override];
+            $parents = [$sub_key, $value];
+            $new_parents = [$sub_key, '/' . $theme_path . '/' . $override];
           }
-          // Remove previous component to be overridden, but keep the attributes.
+          // Remove asset to be overridden, but keep its attributes.
           $attributes = NestedArray::getValue($libraries[$name], $parents);
           NestedArray::unsetValue($libraries[$name], $parents);
           if ($override) {
diff --git a/core/lib/Drupal/Core/Theme/ActiveTheme.php b/core/lib/Drupal/Core/Theme/ActiveTheme.php
index a282434..73f40af 100644
--- a/core/lib/Drupal/Core/Theme/ActiveTheme.php
+++ b/core/lib/Drupal/Core/Theme/ActiveTheme.php
@@ -67,7 +67,7 @@ class ActiveTheme {
   protected $libraries;
 
   /**
-   * The libraries or library components overridden by the theme.
+   * The libraries or library assets overridden by the theme.
    *
    * @var array
    */
@@ -169,9 +169,10 @@ public function getBaseThemes() {
   }
 
   /**
-   * Returns the libraries or library components overridden by the active theme.
+   * Returns the libraries or library assets overridden by the active theme.
    */
   public function getLibrariesOverride() {
     return $this->librariesOverride;
   }
+
 }
diff --git a/core/lib/Drupal/Core/Theme/ThemeInitialization.php b/core/lib/Drupal/Core/Theme/ThemeInitialization.php
index 7231610..c94826c 100644
--- a/core/lib/Drupal/Core/Theme/ThemeInitialization.php
+++ b/core/lib/Drupal/Core/Theme/ThemeInitialization.php
@@ -166,7 +166,7 @@ public function getActiveTheme(Extension $theme, array $base_themes = []) {
     // modules.
     $values['libraries_override'] = array();
 
-    // Grab libraries-overrides from base theme.
+    // Get libraries-override declared by base theme.
     foreach ($base_themes as $base) {
       if (!empty($base->info['libraries-override'])) {
         foreach ($base->info['libraries-override'] as $library => $override) {
@@ -175,7 +175,7 @@ public function getActiveTheme(Extension $theme, array $base_themes = []) {
       }
     }
 
-    // Add libraries-overrides declared by this theme.
+    // Add libraries-override declared by this theme.
     if (!empty($theme->info['libraries-override'])) {
       foreach ($theme->info['libraries-override'] as $library => $override) {
         $values['libraries_override'][$library] = $override;
diff --git a/core/modules/system/src/Tests/Asset/LibraryDiscoveryIntegrationTest.php b/core/modules/system/src/Tests/Asset/LibraryDiscoveryIntegrationTest.php
index 5148824..9ce30b8 100644
--- a/core/modules/system/src/Tests/Asset/LibraryDiscoveryIntegrationTest.php
+++ b/core/modules/system/src/Tests/Asset/LibraryDiscoveryIntegrationTest.php
@@ -8,6 +8,8 @@
 namespace Drupal\system\Tests\Asset;
 
 use Drupal\Component\Utility\SafeMarkup;
+use Drupal\Core\Extension\Extension;
+use Drupal\Core\Theme\ActiveTheme;
 use Drupal\simpletest\KernelTestBase;
 
 /**
@@ -43,7 +45,6 @@ public function testElementInfoByTheme() {
     $this->assertTrue($library_discovery->getLibraryByName('test_theme', 'kitten'));
   }
 
-
   /**
    * Tests that libraries-overrides are applied to library definitions.
    */
@@ -62,27 +63,91 @@ public function testLibrariesOverride() {
     // Assert that entire library was correctly overridden.
     $this->assertEqual($library_discovery->getLibraryByName('core', 'drupal.collapse'), $library_discovery->getLibraryByName('test_theme', 'collapse'), 'Entire library correctly overridden.');
 
-    // Assert that library component was correctly overridden.
+    // Assert that library asset was correctly overridden.
     $library = $library_discovery->getLibraryByName('classy', 'base');
     $this->assertAssetInLibraryComponent($library['css'], 'base', 'core/modules/system/tests/themes/test_theme/css/test_theme_layout.css');
 
     // Assert that entire library was correctly removed.
     $this->assertFalse($library_discovery->getLibraryByName('core', 'drupal.progress'), 'Entire library correctly removed.');
 
-    // Assert that library component was correctly removed.
+    // Assert that library asset was correctly removed.
     $library = $library_discovery->getLibraryByName('core', 'drupal.dialog');
     $this->assertNoAssetInLibraryComponent($library['css'], 'drupal.dialog', 'core/misc/dialog.theme.css');
 
-    // Assert that overridden library component still retains attributes.
+    // Assert that overridden library asset still retains attributes.
     $library = $library_discovery->getLibraryByName('core', 'jquery');
     foreach ($library['js'] as $definition) {
       if ($definition['data'] == 'core/modules/system/tests/themes/test_theme/js/collapse.js') {
-        $this->assertEqual($definition['minified'] && $definition['weight'] == -20, 'Previous attributes retained');
+        $this->assertTrue($definition['minified'] && $definition['weight'] == -20, 'Previous attributes retained');
         break;
       }
     }
   }
 
+  /**
+   * Tests libraries-override on drupalSettings.
+   */
+  public function testLibrariesOverrideDrupalSettings() {
+    $this->container->get('theme_handler')->install(['test_theme_libraries_override_with_drupal_settings']);
+
+    /** @var \Drupal\Core\Theme\ThemeInitializationInterface $theme_initializer */
+    $theme_initializer = $this->container->get('theme.initialization');
+
+    /** @var \Drupal\Core\Theme\ThemeManagerInterface $theme_manager */
+    $theme_manager = $this->container->get('theme.manager');
+
+    /** @var \Drupal\Core\Render\ElementInfoManagerInterface $element_info */
+    $library_discovery = $this->container->get('library.discovery');
+
+    $theme_manager->setActiveTheme($theme_initializer->getActiveThemeByName('test_theme_libraries_override_with_drupal_settings'));
+
+    // Assert that drupalSettings cannot be overridden and throws an exception.
+    try {
+      $library_discovery->getLibraryByName('core', 'drupal.ajax');
+      $this->fail('Throw LogicException when trying to override drupalSettings');
+    }
+    catch (\LogicException $e) {
+      if ($e->getMessage() === 'drupalSettings cannot be overridden in libraries-override. Trying to override <em class="placeholder">core/drupal.ajax/drupalSettings/ajaxPageState</em>.') {
+        $this->pass('Throw LogicException when trying to override drupalSettings');
+      }
+      else {
+        $this->fail('Throw LogicException when trying to override drupalSettings');
+      }
+    }
+  }
+
+  /**
+   * Tests libraries-override on malformed assets.
+   */
+  public function testLibrariesOverrideMalformedAsset() {
+    $this->container->get('theme_handler')->install(['test_theme_libraries_override_with_invalid_asset']);
+
+    /** @var \Drupal\Core\Theme\ThemeInitializationInterface $theme_initializer */
+    $theme_initializer = $this->container->get('theme.initialization');
+
+    /** @var \Drupal\Core\Theme\ThemeManagerInterface $theme_manager */
+    $theme_manager = $this->container->get('theme.manager');
+
+    /** @var \Drupal\Core\Render\ElementInfoManagerInterface $element_info */
+    $library_discovery = $this->container->get('library.discovery');
+
+    $theme_manager->setActiveTheme($theme_initializer->getActiveThemeByName('test_theme_libraries_override_with_invalid_asset'));
+
+    // Assert that improperly formed asset "specs" throw an exception.
+    try {
+      $library_discovery->getLibraryByName('core', 'drupal.dialog');
+      $this->fail('Throw LogicException when specifying invalid override');
+    }
+    catch (\LogicException $e) {
+      if ($e->getMessage() === 'Library asset <em class="placeholder">core/drupal.dialog/css</em> is not correctly specified.') {
+        $this->pass('Throw LogicException when specifying invalid override');
+      }
+      else {
+        $this->fail('Throw LogicException when specifying invalid override');
+      }
+    }
+  }
+
   protected function assertAssetInLibraryComponent($component, $library_name, $asset, $message = NULL) {
     if (!isset($message)) {
       $message = SafeMarkup::format('Asset @asset found in library @library', ['@asset' => $asset, '@library' => $library_name]);
diff --git a/core/modules/system/tests/themes/test_theme/css/collapse.css b/core/modules/system/tests/themes/test_theme/css/collapse.css
index a774ab4..c781141 100644
--- a/core/modules/system/tests/themes/test_theme/css/collapse.css
+++ b/core/modules/system/tests/themes/test_theme/css/collapse.css
@@ -1,4 +1,4 @@
 /**
  * @file
- * Test css asset file for test_theme.theme
+ * Test CSS asset file for test_theme.theme
  */
diff --git a/core/modules/system/tests/themes/test_theme/js/collapse.js b/core/modules/system/tests/themes/test_theme/js/collapse.js
index 05e01dd..bfb509c 100644
--- a/core/modules/system/tests/themes/test_theme/js/collapse.js
+++ b/core/modules/system/tests/themes/test_theme/js/collapse.js
@@ -1,4 +1,4 @@
 /**
  * @file
- * Test js asset file for test_theme.theme
+ * Test JS asset file for test_theme.theme
  */
diff --git a/core/modules/system/tests/themes/test_theme/test_theme.info.yml b/core/modules/system/tests/themes/test_theme/test_theme.info.yml
index abfdc65..e285cd7 100644
--- a/core/modules/system/tests/themes/test_theme/test_theme.info.yml
+++ b/core/modules/system/tests/themes/test_theme/test_theme.info.yml
@@ -24,10 +24,9 @@ libraries-override:
   classy/base/css/theme/css/layout.css: css/test_theme_layout.css
   # Remove one particular asset.
   core/drupal.dialog/css/theme/misc/dialog.theme.css: false
-  # It works for js as well.
+  # It works for JS as well.
   core/jquery/js/assets/vendor/jquery/jquery.min.js: js/collapse.js
 regions:
   content: Content
   left: Left
   right: Right
-
diff --git a/core/modules/system/tests/themes/test_theme_libraries_override_with_drupal_settings/test_theme_libraries_override_with_drupal_settings.info.yml b/core/modules/system/tests/themes/test_theme_libraries_override_with_drupal_settings/test_theme_libraries_override_with_drupal_settings.info.yml
new file mode 100644
index 0000000..0939c27
--- /dev/null
+++ b/core/modules/system/tests/themes/test_theme_libraries_override_with_drupal_settings/test_theme_libraries_override_with_drupal_settings.info.yml
@@ -0,0 +1,9 @@
+name: 'Test theme libraries-override'
+type: theme
+description: 'Theme with drupalSettings libraries-override'
+version: VERSION
+base theme: classy
+core: 8.x
+libraries-override:
+  # drupalSettings libraries override. Should throw a \LogicException.
+  core/drupal.ajax/drupalSettings/ajaxPageState: { }
diff --git a/core/modules/system/tests/themes/test_theme_libraries_override_with_invalid_asset/test_theme_libraries_override_with_invalid_asset.info.yml b/core/modules/system/tests/themes/test_theme_libraries_override_with_invalid_asset/test_theme_libraries_override_with_invalid_asset.info.yml
new file mode 100644
index 0000000..ecba74e
--- /dev/null
+++ b/core/modules/system/tests/themes/test_theme_libraries_override_with_invalid_asset/test_theme_libraries_override_with_invalid_asset.info.yml
@@ -0,0 +1,9 @@
+name: 'Test theme libraries-override'
+type: theme
+description: 'Theme with invalid libraries-override asset spec.'
+version: VERSION
+base theme: classy
+core: 8.x
+libraries-override:
+  # A malformed library asset name. Should throw a \LogicException.
+  core/drupal.dialog/css: false