diff -u b/core/lib/Drupal/Core/Cache/DatabaseBackend.php b/core/lib/Drupal/Core/Cache/DatabaseBackend.php
--- b/core/lib/Drupal/Core/Cache/DatabaseBackend.php
+++ b/core/lib/Drupal/Core/Cache/DatabaseBackend.php
@@ -42,6 +42,13 @@
   protected $checksumProvider;
 
   /**
+   * The transliteration service.
+   *
+   * @var \Drupal\Component\Transliteration\TransliterationInterface
+   */
+  protected $transliteration;
+
+  /**
    * Constructs a DatabaseBackend object.
    *
    * @param \Drupal\Core\Database\Connection $connection
@@ -419,20 +426,36 @@
    *   The passed in cache ID.
    *
    * @return string
-   *   A cache ID that is at most 255 characters long.
+   *   An ASCII-encoded cache ID that is at most 255 characters long.
    */
   protected function normalizeCid($cid) {
-    // Nothing to do if the ID length is 255 characters or less.
-    if (strlen($cid) <= 255) {
+    // Nothing to do if the ID is a US ASCII string of 255 characters or less.
+    $cid_is_ascii = mb_check_encoding($cid, 'ASCII');
+    if (strlen($cid) <= 255 && $cid_is_ascii) {
       return $cid;
     }
     // Return a string that uses as much as possible of the original cache ID
     // with the hash appended.
     $hash = Crypt::hashBase64($cid);
+    if (!$cid_is_ascii) {
+      $cid = $this->transliteration()->transliterate($cid);
+    }
     return substr($cid, 0, 255 - strlen($hash)) . $hash;
   }
 
   /**
+   * Wraps the transliteration service.
+   *
+   * @return \Drupal\Component\Transliteration\TransliterationInterface
+   */
+  protected function transliteration() {
+    if (!$this->transliteration) {
+      $this->transliteration = \Drupal::transliteration();
+    }
+    return $this->transliteration;
+  }
+
+  /**
    * Defines the schema for the {cache_*} bin tables.
    */
   public function schemaDefinition() {
diff -u b/core/lib/Drupal/Core/Database/Driver/pgsql/Schema.php b/core/lib/Drupal/Core/Database/Driver/pgsql/Schema.php
--- b/core/lib/Drupal/Core/Database/Driver/pgsql/Schema.php
+++ b/core/lib/Drupal/Core/Database/Driver/pgsql/Schema.php
@@ -364,6 +364,7 @@
     // $map does not use drupal_static as its value never changes.
     static $map = array(
       'varchar_ascii:normal' => 'varchar',
+
       'varchar:normal' => 'varchar',
       'char:normal' => 'character',
 
only in patch2:
unchanged:
--- a/core/modules/system/src/Tests/Cache/DatabaseBackendUnitTest.php
+++ b/core/modules/system/src/Tests/Cache/DatabaseBackendUnitTest.php
@@ -33,4 +33,24 @@ protected function createCacheBackend($bin) {
     return new DatabaseBackend($this->container->get('database'), $this->container->get('cache_tags.invalidator.checksum'), $bin);
   }
 
+  /**
+   * {@inheritdoc}
+   */
+  public function testSetGet() {
+    parent::testSetGet();
+    $backend = $this->getCacheBackend();
+
+    // Set up a cache ID that is not ASCII and longer than 255 characters so we
+    // can test cache ID normalization.
+    $cid_long = str_repeat('愛€', 500);
+    $cached_value_long = $this->randomMachineName();
+    $backend->set($cid_long, $cached_value_long);
+    $this->assertIdentical($cached_value_long, $backend->get($cid_long)->data, "Backend contains the correct value for long, non-ASCII cache id.");
+
+    $cid_short = '愛1€';
+    $cached_value_short = $this->randomMachineName();
+    $backend->set($cid_short, $cached_value_short);
+    $this->assertIdentical($cached_value_short, $backend->get($cid_short)->data, "Backend contains the correct value for short, non-ASCII cache id.");
+  }
+
 }