diff --git a/core/includes/bootstrap.inc b/core/includes/bootstrap.inc
index 6137a34..98dae85 100644
--- a/core/includes/bootstrap.inc
+++ b/core/includes/bootstrap.inc
@@ -10,7 +10,7 @@
 use Drupal\Component\Utility\SafeMarkup;
 use Drupal\Component\Utility\Unicode;
 use Drupal\Core\Config\BootstrapConfigStorageFactory;
-use Drupal\Core\Extension\UnknownExtensionException;
+use Drupal\Core\Extension\Exception\UnknownExtensionException;
 use Drupal\Core\Logger\RfcLogLevel;
 use Drupal\Core\Test\TestDatabase;
 use Drupal\Core\Session\AccountInterface;
diff --git a/core/lib/Drupal/Core/Extension/Exception/UninstalledExtensionException.php b/core/lib/Drupal/Core/Extension/Exception/UninstalledExtensionException.php
index 0f495ee..8cfb9bf 100644
--- a/core/lib/Drupal/Core/Extension/Exception/UninstalledExtensionException.php
+++ b/core/lib/Drupal/Core/Extension/Exception/UninstalledExtensionException.php
@@ -1,6 +1,6 @@
 <?php
 
-namespace Drupal\Core\Extension;
+namespace Drupal\Core\Extension\Exception;
 
 /**
  * Exception class thrown when a specified extension has not been installed.
diff --git a/core/lib/Drupal/Core/Extension/Exception/UnknownExtensionException.php b/core/lib/Drupal/Core/Extension/Exception/UnknownExtensionException.php
index a139540..7daa4d1 100644
--- a/core/lib/Drupal/Core/Extension/Exception/UnknownExtensionException.php
+++ b/core/lib/Drupal/Core/Extension/Exception/UnknownExtensionException.php
@@ -1,6 +1,6 @@
 <?php
 
-namespace Drupal\Core\Extension;
+namespace Drupal\Core\Extension\Exception;
 
 /**
  * Exception class thrown when a specified extension is not on the filesystem.
diff --git a/core/lib/Drupal/Core/Extension/ExtensionList.php b/core/lib/Drupal/Core/Extension/ExtensionList.php
index 864bd16..6b5dfec 100644
--- a/core/lib/Drupal/Core/Extension/ExtensionList.php
+++ b/core/lib/Drupal/Core/Extension/ExtensionList.php
@@ -4,6 +4,7 @@
 
 use Drupal\Core\Cache\CacheBackendInterface;
 use Drupal\Core\Database\DatabaseExceptionWrapper;
+use Drupal\Core\Extension\Exception\UnknownExtensionException;
 use Drupal\Core\State\StateInterface;
 
 /**
@@ -227,7 +228,7 @@ public function exists($extension_name) {
    * @return string
    *   The human-readable name of the extension.
    *
-   * @throws \Drupal\Core\Extension\UnknownExtensionException
+   * @throws \Drupal\Core\Extension\Exception\UnknownExtensionException
    *   If there is no extension with the supplied machine name.
    */
   public function getName($extension_name) {
@@ -244,7 +245,7 @@ public function getName($extension_name) {
    *   A processed extension object for the extension with the specified machine
    *   name.
    *
-   * @throws \Drupal\Core\Extension\UnknownExtensionException
+   * @throws \Drupal\Core\Extension\Exception\UnknownExtensionException
    *   If there is no extension with the supplied name.
    */
   public function get($extension_name) {
@@ -334,7 +335,7 @@ protected function doList() {
    * @return mixed[]
    *   An associative array of extension information.
    *
-   * @throws \Drupal\Core\Extension\UnknownExtensionException
+   * @throws \Drupal\Core\Extension\Exception\UnknownExtensionException
    *   If there is no extension with the supplied name.
    */
   public function getExtensionInfo($extension_name) {
@@ -505,7 +506,7 @@ public function setPathname($extension_name, $pathname) {
    *   The drupal-root relative filename and path of the requested extension's
    *   .info.yml file.
    *
-   * @throws \Drupal\Core\Extension\UnknownExtensionException
+   * @throws \Drupal\Core\Extension\Exception\UnknownExtensionException
    *   If there is no extension with the supplied machine name.
    */
   public function getPathname($extension_name) {
@@ -533,7 +534,7 @@ public function getPathname($extension_name) {
    * @return string
    *   The Drupal-root-relative path to the specified extension.
    *
-   * @throws \Drupal\Core\Extension\UnknownExtensionException
+   * @throws \Drupal\Core\Extension\Exception\UnknownExtensionException
    *   If there is no extension with the supplied name.
    */
   public function getPath($extension_name) {
diff --git a/core/lib/Drupal/Core/Extension/ThemeHandler.php b/core/lib/Drupal/Core/Extension/ThemeHandler.php
index fdaf585..c83477d 100644
--- a/core/lib/Drupal/Core/Extension/ThemeHandler.php
+++ b/core/lib/Drupal/Core/Extension/ThemeHandler.php
@@ -3,6 +3,7 @@
 namespace Drupal\Core\Extension;
 
 use Drupal\Core\Config\ConfigFactoryInterface;
+use Drupal\Core\Extension\Exception\UninstalledExtensionException;
 use Drupal\Core\State\StateInterface;
 
 /**
diff --git a/core/lib/Drupal/Core/Extension/ThemeHandlerInterface.php b/core/lib/Drupal/Core/Extension/ThemeHandlerInterface.php
index a80831e..f25666d 100644
--- a/core/lib/Drupal/Core/Extension/ThemeHandlerInterface.php
+++ b/core/lib/Drupal/Core/Extension/ThemeHandlerInterface.php
@@ -39,7 +39,7 @@ public function install(array $theme_list, $install_dependencies = TRUE);
    * @param array $theme_list
    *   The themes to uninstall.
    *
-   * @throws \Drupal\Core\Extension\UninstalledExtensionException
+   * @throws \Drupal\Core\Extension\Exception\UninstalledExtensionException
    *   Thrown when you try to uninstall a theme that wasn't installed.
    *
    * @see hook_themes_uninstalled()
diff --git a/core/tests/Drupal/KernelTests/Core/Theme/ThemeInstallerTest.php b/core/tests/Drupal/KernelTests/Core/Theme/ThemeInstallerTest.php
index 795a51d..dc606de 100644
--- a/core/tests/Drupal/KernelTests/Core/Theme/ThemeInstallerTest.php
+++ b/core/tests/Drupal/KernelTests/Core/Theme/ThemeInstallerTest.php
@@ -4,7 +4,7 @@
 
 use Drupal\Core\DependencyInjection\ContainerBuilder;
 use Drupal\Core\Extension\ExtensionNameLengthException;
-use Drupal\Core\Extension\UnknownExtensionException;
+use Drupal\Core\Extension\Exception\UnknownExtensionException;
 use Drupal\KernelTests\KernelTestBase;
 
 /**
diff --git a/core/tests/Drupal/Tests/Core/Extension/ExtensionListTest.php b/core/tests/Drupal/Tests/Core/Extension/ExtensionListTest.php
index d0450ab..565bb65 100644
--- a/core/tests/Drupal/Tests/Core/Extension/ExtensionListTest.php
+++ b/core/tests/Drupal/Tests/Core/Extension/ExtensionListTest.php
@@ -9,7 +9,7 @@
 use Drupal\Core\Extension\ExtensionList;
 use Drupal\Core\Extension\InfoParserInterface;
 use Drupal\Core\Extension\ModuleHandlerInterface;
-use Drupal\Core\Extension\UnknownExtensionException;
+use Drupal\Core\Extension\Exception\UnknownExtensionException;
 use Drupal\Core\State\StateInterface;
 use Drupal\Tests\UnitTestCase;
 use org\bovigo\vfs\vfsStream;
diff --git a/core/tests/Drupal/Tests/Core/Extension/ModuleHandlerTest.php b/core/tests/Drupal/Tests/Core/Extension/ModuleHandlerTest.php
index 13d3e93..f5d9f7e 100644
--- a/core/tests/Drupal/Tests/Core/Extension/ModuleHandlerTest.php
+++ b/core/tests/Drupal/Tests/Core/Extension/ModuleHandlerTest.php
@@ -5,7 +5,7 @@
 use Drupal\Core\Cache\CacheBackendInterface;
 use Drupal\Core\Extension\Extension;
 use Drupal\Core\Extension\ModuleHandler;
-use Drupal\Core\Extension\UnknownExtensionException;
+use Drupal\Core\Extension\Exception\UnknownExtensionException;
 use Drupal\Tests\UnitTestCase;
 
 /**