diff --git a/src/Symfony/Component/Routing/Loader/Configurator/ImportConfigurator.php b/src/Symfony/Component/Routing/Loader/Configurator/ImportConfigurator.php
index f11b795752..0059a632a1 100644
--- a/src/Symfony/Component/Routing/Loader/Configurator/ImportConfigurator.php
+++ b/src/Symfony/Component/Routing/Loader/Configurator/ImportConfigurator.php
@@ -13,6 +13,7 @@ namespace Symfony\Component\Routing\Loader\Configurator;
 
 use Symfony\Component\Routing\Route;
 use Symfony\Component\Routing\RouteCollection;
+use Symfony\Component\Routing\RouteCompiler;
 
 /**
  * @author Nicolas Grekas <p@tchwork.com>
@@ -63,6 +64,7 @@ class ImportConfigurator
                     foreach ($prefix as $locale => $localePrefix) {
                         $localizedRoute = clone $route;
                         $localizedRoute->setDefault('_locale', $locale);
+                        $localizedRoute->setRequirement('_locale', preg_quote($locale, RouteCompiler::REGEX_DELIMITER));
                         $localizedRoute->setDefault('_canonical_route', $name);
                         $localizedRoute->setPath($localePrefix.(!$trailingSlashOnRoot && '/' === $route->getPath() ? '' : $route->getPath()));
                         $this->route->add($name.'.'.$locale, $localizedRoute);
diff --git a/src/Symfony/Component/Routing/Loader/XmlFileLoader.php b/src/Symfony/Component/Routing/Loader/XmlFileLoader.php
index 49b552d627..31c614950e 100644
--- a/src/Symfony/Component/Routing/Loader/XmlFileLoader.php
+++ b/src/Symfony/Component/Routing/Loader/XmlFileLoader.php
@@ -211,6 +211,7 @@ class XmlFileLoader extends FileLoader
                             $localizedRoute = clone $route;
                             $localizedRoute->setPath($localePrefix.(!$trailingSlashOnRoot && '/' === $route->getPath() ? '' : $route->getPath()));
                             $localizedRoute->setDefault('_locale', $locale);
+                            $localizedRoute->setRequirement('_locale', preg_quote($locale, RouteCompiler::REGEX_DELIMITER));
                             $localizedRoute->setDefault('_canonical_route', $name);
                             $subCollection->add($name.'.'.$locale, $localizedRoute);
                         }
diff --git a/src/Symfony/Component/Routing/Loader/YamlFileLoader.php b/src/Symfony/Component/Routing/Loader/YamlFileLoader.php
index 868da9bd30..8d4b9abdb1 100644
--- a/src/Symfony/Component/Routing/Loader/YamlFileLoader.php
+++ b/src/Symfony/Component/Routing/Loader/YamlFileLoader.php
@@ -216,6 +216,7 @@ class YamlFileLoader extends FileLoader
                         foreach ($prefix as $locale => $localePrefix) {
                             $localizedRoute = clone $route;
                             $localizedRoute->setDefault('_locale', $locale);
+                            $localizedRoute->setRequirement('_locale', preg_quote($locale, RouteCompiler::REGEX_DELIMITER));
                             $localizedRoute->setDefault('_canonical_route', $name);
                             $localizedRoute->setPath($localePrefix.(!$trailingSlashOnRoot && '/' === $route->getPath() ? '' : $route->getPath()));
                             $subCollection->add($name.'.'.$locale, $localizedRoute);
diff --git a/src/Symfony/Component/Routing/Tests/Fixtures/php_dsl_sub_i18n.php b/src/Symfony/Component/Routing/Tests/Fixtures/php_dsl_sub_i18n.php
index e79edc869d..e6d846dd46 100644
--- a/src/Symfony/Component/Routing/Tests/Fixtures/php_dsl_sub_i18n.php
+++ b/src/Symfony/Component/Routing/Tests/Fixtures/php_dsl_sub_i18n.php
@@ -8,4 +8,6 @@ return function (RoutingConfigurator $routes) {
 
     $add('foo', ['fr' => '/foo']);
     $add('bar', ['fr' => '/bar']);
+
+    $routes->add('non_localized', '/non-localized');
 };
diff --git a/src/Symfony/Component/Routing/Tests/Loader/PhpFileLoaderTest.php b/src/Symfony/Component/Routing/Tests/Loader/PhpFileLoaderTest.php
index 789848c660..b84d5ff354 100644
--- a/src/Symfony/Component/Routing/Tests/Loader/PhpFileLoaderTest.php
+++ b/src/Symfony/Component/Routing/Tests/Loader/PhpFileLoaderTest.php
@@ -234,6 +234,7 @@ class PhpFileLoaderTest extends TestCase
         $expectedCollection->add('baz.en', (new Route('/baz'))->setDefaults(['_locale' => 'en', '_canonical_route' => 'baz'])->setRequirement('_locale', 'en'));
         $expectedCollection->add('c_foo.fr', (new Route('/ench/pub/foo'))->setDefaults(['_locale' => 'fr', '_canonical_route' => 'c_foo'])->setRequirement('_locale', 'fr'));
         $expectedCollection->add('c_bar.fr', (new Route('/ench/pub/bar'))->setDefaults(['_locale' => 'fr', '_canonical_route' => 'c_bar'])->setRequirement('_locale', 'fr'));
+        $expectedCollection->add('non_localized.fr', (new Route('/ench/non-localized'))->setDefaults(['_locale' => 'fr', '_canonical_route' => 'non_localized'])->setRequirement('_locale', 'fr'));
 
         $expectedCollection->addResource(new FileResource(realpath(__DIR__.'/../Fixtures/php_dsl_sub_i18n.php')));
         $expectedCollection->addResource(new FileResource(realpath(__DIR__.'/../Fixtures/php_dsl_i18n.php')));
diff --git a/src/Symfony/Component/Routing/Tests/Loader/XmlFileLoaderTest.php b/src/Symfony/Component/Routing/Tests/Loader/XmlFileLoaderTest.php
index 02e1e14d4a..383cda0176 100644
--- a/src/Symfony/Component/Routing/Tests/Loader/XmlFileLoaderTest.php
+++ b/src/Symfony/Component/Routing/Tests/Loader/XmlFileLoaderTest.php
@@ -201,6 +201,9 @@ class XmlFileLoaderTest extends TestCase
 
         $this->assertEquals('/le-prefix/suffix', $routeCollection->get('imported.fr')->getPath());
         $this->assertEquals('/the-prefix/suffix', $routeCollection->get('imported.en')->getPath());
+
+        $this->assertSame('fr', $routeCollection->get('imported.fr')->getRequirement('_locale'));
+        $this->assertSame('en', $routeCollection->get('imported.en')->getRequirement('_locale'));
     }
 
     /**
diff --git a/src/Symfony/Component/Routing/Tests/Loader/YamlFileLoaderTest.php b/src/Symfony/Component/Routing/Tests/Loader/YamlFileLoaderTest.php
index 3878663e6b..e5571b0b7a 100644
--- a/src/Symfony/Component/Routing/Tests/Loader/YamlFileLoaderTest.php
+++ b/src/Symfony/Component/Routing/Tests/Loader/YamlFileLoaderTest.php
@@ -334,6 +334,9 @@ class YamlFileLoaderTest extends TestCase
         $this->assertCount(2, $routes);
         $this->assertEquals('/nl/imported', $routes->get('imported.nl')->getPath());
         $this->assertEquals('/en/imported', $routes->get('imported.en')->getPath());
+
+        $this->assertSame('nl', $routes->get('imported.nl')->getRequirement('_locale'));
+        $this->assertSame('en', $routes->get('imported.en')->getRequirement('_locale'));
     }
 
     public function testImportingRoutesWithOfficialLocales()