diff --git a/core/lib/Drupal/Core/Database/Database.php b/core/lib/Drupal/Core/Database/Database.php
index b611cdc..0e2fab2 100644
--- a/core/lib/Drupal/Core/Database/Database.php
+++ b/core/lib/Drupal/Core/Database/Database.php
@@ -503,11 +503,13 @@ public static function getConnectionInfoAsUrl($key = 'default') {
 
     $namespace = isset($db_info['default']['namespace']) ? $db_info['default']['namespace'] : NULL;
     $driver_class = static::getDatabaseConnectionClass($db_info['default']['driver'], $namespace);
-    $uri = new Uri(NULL);
-    $uri = $uri
-      ->withScheme($db_info['default']['driver'])
-      ->withHost($db_info['default']['host'])
-      ->withPath($db_info['default']['database']);
+
+    // Some database driver do not need a host setting to work but in order to
+    // be converted into a URL they do.
+    $host = isset($db_info['default']['host']) ? $db_info['default']['host'] : 'localhost';
+
+    // Create a URI with the minimum requirement of driver://host/database.
+    $uri = new Uri($db_info['default']['driver'] . '://' . $host . '/' . $db_info['default']['database']);
 
     if (!empty($db_info['default']['prefix']['default'])) {
       $uri = $uri->withFragment($db_info['default']['prefix']['default']);
diff --git a/core/lib/Drupal/Core/Database/Driver/sqlite/Connection.php b/core/lib/Drupal/Core/Database/Driver/sqlite/Connection.php
index daaf828..1896dd7 100644
--- a/core/lib/Drupal/Core/Database/Driver/sqlite/Connection.php
+++ b/core/lib/Drupal/Core/Database/Driver/sqlite/Connection.php
@@ -425,6 +425,8 @@ public static function convertDbUrlToConnectionInfoHelper(Uri $uri, $root, array
     if ($database['database'][0] !== '/') {
       $database['database'] = $root . '/' . $database['database'];
     }
+    // The host setting is meaningless for SQLite databases.
+    unset($database['host']);
     return $database;
   }
 
diff --git a/core/modules/simpletest/simpletest.module b/core/modules/simpletest/simpletest.module
index 4dc7544..d589466 100644
--- a/core/modules/simpletest/simpletest.module
+++ b/core/modules/simpletest/simpletest.module
@@ -262,9 +262,11 @@ function simpletest_phpunit_configuration_filepath() {
  *  The results as returned by exec().
  */
 function simpletest_phpunit_run_command(array $unescaped_test_classnames, $phpunit_file, &$status = NULL) {
-  // Setup an environment variable containing the database connection so that
-  // functional tests can connect to the database.
-  putenv('SIMPLETEST_DB=' . Database::getConnectionInfoAsUrl());
+  if (Database::getConnectionInfo()) {
+    // Setup an environment variable containing the database connection so that
+    // functional tests can connect to the database.
+    putenv('SIMPLETEST_DB=' . Database::getConnectionInfoAsUrl());
+  }
   $phpunit_bin = simpletest_phpunit_command();
 
   $command = array(
diff --git a/core/tests/Drupal/Tests/Core/Database/DatabaseTest.php b/core/tests/Drupal/Tests/Core/Database/DatabaseTest.php
index 6046ab5..7c17d06 100644
--- a/core/tests/Drupal/Tests/Core/Database/DatabaseTest.php
+++ b/core/tests/Drupal/Tests/Core/Database/DatabaseTest.php
@@ -56,7 +56,6 @@ public function providerTestconvertDbUrlToConnectionInfo() {
       'sqlite://localhost/database_file',
       [
         'driver' => 'sqlite',
-        'host' => 'localhost',
         'database' => '/root/database_file',
         'prefix' => NULL,
         'namespace' => '',
@@ -88,7 +87,6 @@ public function providerGetConnectionInfoAsUrl() {
       'sqlite://localhost/database_file',
       [
         'driver' => 'sqlite',
-        'host' => 'localhost',
         'database' => 'database_file',
         'prefix' => NULL,
         'namespace' => '',
@@ -143,7 +141,6 @@ protected function baseConnectionConvertProviderData() {
         'sqlite://localhost//absolute/database_file',
         [
           'driver' => 'sqlite',
-          'host' => 'localhost',
           'database' => '/absolute/database_file',
           'prefix' => NULL,
           'namespace' => '',