diff --git a/core/lib/Drupal/Core/Path/AliasStorage.php b/core/lib/Drupal/Core/Path/AliasStorage.php
index e702f55..657f928 100644
--- a/core/lib/Drupal/Core/Path/AliasStorage.php
+++ b/core/lib/Drupal/Core/Path/AliasStorage.php
@@ -14,6 +14,9 @@
 
 /**
  * Provides a class for CRUD operations on path aliases.
+ *
+ * All queries use case-insensitive implementations, so '/test-alias' and
+ * '/test-Alias' is treated as equal.
  */
 class AliasStorage implements AliasStorageInterface {
   /**
diff --git a/core/lib/Drupal/Core/Path/AliasStorageInterface.php b/core/lib/Drupal/Core/Path/AliasStorageInterface.php
index 7717aef..a416fec 100644
--- a/core/lib/Drupal/Core/Path/AliasStorageInterface.php
+++ b/core/lib/Drupal/Core/Path/AliasStorageInterface.php
@@ -44,6 +44,8 @@ public function save($source, $alias, $langcode = LanguageInterface::LANGCODE_NO
   /**
    * Fetches a specific URL alias from the database.
    *
+   * The default implementation provides a case-insensitive implementation.
+   *
    * @param array $conditions
    *   An array of query conditions.
    *
@@ -60,6 +62,8 @@ public function load($conditions);
   /**
    * Deletes a URL alias.
    *
+   * The default implementation provides a case-insensitive implementation.
+   *
    * @param array $conditions
    *   An array of criteria.
    */
@@ -82,6 +86,8 @@ public function preloadPathAlias($preloaded, $langcode);
   /**
    * Returns an alias of Drupal system URL.
    *
+   * The default implementation provides a case-insensitive implementation.
+   *
    * @param string $path
    *   The path to investigate for corresponding path aliases.
    * @param string $langcode
@@ -96,6 +102,8 @@ public function lookupPathAlias($path, $langcode);
   /**
    * Returns Drupal system URL of an alias.
    *
+   * The default implementation provides a case-insensitive implementation.
+   *
    * @param string $path
    *   The path to investigate for corresponding system URLs.
    * @param string $langcode
@@ -110,6 +118,8 @@ public function lookupPathSource($path, $langcode);
   /**
    * Checks if alias already exists.
    *
+   * The default implementation provides a case-insensitive implementation.
+   *
    * @param string $alias
    *   Alias to check against.
    * @param string $langcode
diff --git a/core/modules/path/src/Form/PathFormBase.php b/core/modules/path/src/Form/PathFormBase.php
index 8c84841..eac4e71 100644
--- a/core/modules/path/src/Form/PathFormBase.php
+++ b/core/modules/path/src/Form/PathFormBase.php
@@ -180,8 +180,16 @@ public function validateForm(array &$form, FormStateInterface $form_state) {
     $langcode = $form_state->getValue('langcode', LanguageInterface::LANGCODE_NOT_SPECIFIED);
 
     if ($this->aliasStorage->aliasExists($alias, $langcode, $this->path['source'])) {
-      $form_state->setErrorByName('alias', t('The alias %alias is already in use in this language.', array('%alias' => $alias)));
+      $stored_alias = $this->aliasStorage->load(['alias' => $alias, 'langocde' => $langcode]);
+      if ($stored_alias['alias'] !== $alias) {
+        $form_state->setErrorByName('alias', t('There is an alias with other case-sensitivity: %actual_alias is already in use in this language.', ['%actual_alias' => $stored_alias['alias']]));
+      }
+      else {
+        $form_state->setErrorByName('alias', t('The alias %alias is already in use in this language.', array('%alias' => $alias)));
+      }
     }
+
+
     if (!$this->pathValidator->isValid(trim($source, '/'))) {
       $form_state->setErrorByName('source', t("The path '@link_path' is either invalid or you do not have access to it.", array('@link_path' => $source)));
     }
diff --git a/core/tests/Drupal/KernelTests/Core/Path/AliasStorageTest.php b/core/tests/Drupal/KernelTests/Core/Path/AliasStorageTest.php
new file mode 100644
index 0000000..98180e3
--- /dev/null
+++ b/core/tests/Drupal/KernelTests/Core/Path/AliasStorageTest.php
@@ -0,0 +1,86 @@
+<?php
+
+/**
+ * @file
+ * Contains \Drupal\KernelTests\Core\Path\AliasStorageTest.
+ */
+
+namespace Drupal\KernelTests\Core\Path;
+
+use Drupal\Core\Language\LanguageInterface;
+use Drupal\KernelTests\KernelTestBase;
+
+/**
+ * @coversDefaultClass \Drupal\Core\Path\AliasStorage
+ * @group path
+ */
+class AliasStorageTest extends KernelTestBase {
+
+  /**
+   * {@inheritdoc}
+   */
+  public static $modules = ['system'];
+
+  /** @var \Drupal\Core\Path\AliasStorage */
+  protected $storage;
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function setUp() {
+    parent::setUp();
+
+    $this->installSchema('system', 'url_alias');
+    $this->storage = $this->container->get('path.alias_storage');
+  }
+
+  /**
+   * @covers ::load
+   */
+  public function testLoad() {
+    $this->storage->save('/test-source-Case', '/test-alias-Case');
+
+    $expected = [
+      'pid' => 1,
+      'alias' => '/test-alias-Case',
+      'source' => '/test-source-Case',
+      'langcode' => LanguageInterface::LANGCODE_NOT_SPECIFIED,
+    ];
+
+    $this->assertEquals($expected, $this->storage->load(['alias' => '/test-alias-Case']));
+    $this->assertEquals($expected, $this->storage->load(['alias' => '/test-alias-case']));
+    $this->assertEquals($expected, $this->storage->load(['source' => '/test-source-Case']));
+    $this->assertEquals($expected, $this->storage->load(['source' => '/test-source-case']));
+  }
+
+  /**
+   * @covers ::lookupPathAlias
+   */
+  public function testLookupPathAlias() {
+    $this->storage->save('/test-source-Case', '/test-alias');
+
+    $this->assertEquals('/test-alias', $this->storage->lookupPathAlias('/test-source-Case', LanguageInterface::LANGCODE_NOT_SPECIFIED));
+    $this->assertEquals('/test-alias', $this->storage->lookupPathAlias('/test-source-case', LanguageInterface::LANGCODE_NOT_SPECIFIED));
+  }
+
+  /**
+   * @covers ::lookupPathSource
+   */
+  public function testLookupPathSource() {
+    $this->storage->save('/test-source', '/test-alias-Case');
+
+    $this->assertEquals('/test-source', $this->storage->lookupPathSource('/test-alias-Case', LanguageInterface::LANGCODE_NOT_SPECIFIED));
+    $this->assertEquals('/test-source', $this->storage->lookupPathSource('/test-alias-case', LanguageInterface::LANGCODE_NOT_SPECIFIED));
+  }
+
+  /**
+   * @covers ::aliasExists
+   */
+  public function testAliasExists() {
+    $this->storage->save('/test-source-Case', '/test-alias-Case');
+
+    $this->assertTrue($this->storage->aliasExists('/test-alias-Case', LanguageInterface::LANGCODE_NOT_SPECIFIED));
+    $this->assertTrue($this->storage->aliasExists('/test-alias-case', LanguageInterface::LANGCODE_NOT_SPECIFIED));
+  }
+
+}