diff --git a/classes/LocaleManager.php b/classes/LocaleManager.php
index 7e36e8c..03531fb 100644
--- a/classes/LocaleManager.php
+++ b/classes/LocaleManager.php
@@ -95,4 +95,13 @@ class LocaleManager
         $this->curLocale = $locale;
         $this->sessionSegment->set('locale', $locale);
     }
+
+    /**
+     * Unset the current locale.
+     */
+    public function unsetLocale()
+    {
+        $this->curLocale = null;
+        $this->sessionSegment->clear('locale');
+    }
 }
diff --git a/tests/LocaleManagerTest.php b/tests/LocaleManagerTest.php
index 7eb5cdb..2808362 100644
--- a/tests/LocaleManagerTest.php
+++ b/tests/LocaleManagerTest.php
@@ -75,4 +75,15 @@ class LocaleManagerTest extends TestCase
         $this->assertInstanceOf(Locale::class, $locale);
         $this->assertEquals('foo_BAR', (string) $locale);
     }
+
+    /**
+     * Test the unsetLocale function.
+     *
+     * @return void
+     */
+    public function testUnsetLocale()
+    {
+        $this->localeManager->unsetLocale();
+        $this->assertNull($this->localeManager->getLocale());
+    }
 }
diff --git a/tests/LocaleMiddlewareTest.php b/tests/LocaleMiddlewareTest.php
index 1845327..35c30e2 100644
--- a/tests/LocaleMiddlewareTest.php
+++ b/tests/LocaleMiddlewareTest.php
@@ -5,6 +5,7 @@
 
 namespace Alltube\Test;
 
+use Alltube\Locale;
 use Alltube\LocaleManager;
 use Alltube\LocaleMiddleware;
 use PHPUnit\Framework\TestCase;
@@ -30,9 +31,19 @@ class LocaleMiddlewareTest extends TestCase
      */
     protected function setUp()
     {
-        $container = new Container();
-        $container['locale'] = new LocaleManager();
-        $this->middleware = new LocaleMiddleware($container);
+        $this->container = new Container();
+        $this->container['locale'] = new LocaleManager();
+        $this->middleware = new LocaleMiddleware($this->container);
+    }
+
+    /**
+     * Unset locale cookie after each test.
+     *
+     * @return void
+     */
+    protected function tearDown()
+    {
+        $this->container['locale']->unsetLocale();
     }
 
     /**
@@ -66,12 +77,29 @@ class LocaleMiddlewareTest extends TestCase
     }
 
     /**
-     * Mock function that does nothing.
+     * Check that the request contains an Accept-Language header.
+     *
+     * @param Request $request PSR-7 request
      *
      * @return void
      */
-    public function nothing()
+    public function assertHeader(Request $request)
     {
+        $header = $request->getHeader('Accept-Language');
+        $this->assertEquals('foo-BAR', $header[0]);
+    }
+
+    /**
+     * Check that the request contains no Accept-Language header.
+     *
+     * @param Request $request PSR-7 request
+     *
+     * @return void
+     */
+    public function assertNoHeader(Request $request)
+    {
+        $header = $request->getHeader('Accept-Language');
+        $this->assertEmpty($header);
     }
 
     /**
@@ -83,14 +111,14 @@ class LocaleMiddlewareTest extends TestCase
     {
         $request = Request::createFromEnvironment(Environment::mock());
         $this->middleware->__invoke(
-            $request->withHeader('Accept-Language', 'fr-FR'),
+            $request->withHeader('Accept-Language', 'foo-BAR'),
             new Response(),
-            [$this, 'nothing']
+            [$this, 'assertHeader']
         );
     }
 
     /**
-     * Test the __invoke() function withot the Accept-Language header.
+     * Test the __invoke() function without the Accept-Language header.
      *
      * @return void
      */
@@ -100,7 +128,7 @@ class LocaleMiddlewareTest extends TestCase
         $this->middleware->__invoke(
             $request->withoutHeader('Accept-Language'),
             new Response(),
-            [$this, 'nothing']
+            [$this, 'assertNoHeader']
         );
     }