diff --git a/classes/mobile/Mobile.class.php b/classes/mobile/Mobile.class.php
index e6bad61ce..ab5135018 100644
--- a/classes/mobile/Mobile.class.php
+++ b/classes/mobile/Mobile.class.php
@@ -73,7 +73,7 @@ class Mobile
 		$uatype = $uahash . ':' . (self::$_ismobile ? '1' : '0');
 		if ($cookie !== $uatype)
 		{
-			setcookie('rx_uatype', $uatype, 0, RX_BASEURL);
+			setcookie('rx_uatype', $uatype, 0, RX_BASEURL, Rhymix\Framework\Session::getDomain());
 			$_COOKIE['rx_uatype'] = $uatype;
 		}
 		
diff --git a/common/framework/session.php b/common/framework/session.php
index 584a87187..2a78f1118 100644
--- a/common/framework/session.php
+++ b/common/framework/session.php
@@ -10,6 +10,8 @@ class Session
 	/**
 	 * Properties for internal use only.
 	 */
+	protected static $_domain = false;
+	protected static $_subdomain = false;
 	protected static $_started = false;
 	protected static $_autologin_key = false;
 	protected static $_member_info = false;
@@ -758,6 +760,48 @@ class Session
 		$_SESSION['RHYMIX']['timezone'] = $timezone;
 	}
 	
+	/**
+	 * Get session domain.
+	 * 
+	 * @return string
+	 */
+	public static function getDomain()
+	{
+		if (self::$_domain || (self::$_domain = Config::get('session.domain')))
+		{
+			return self::$_domain;
+		}
+		else
+		{
+			self::$_domain = ini_get('session.cookie_domain') ?: preg_replace('/:\\d+$/', '', strtolower($_SERVER['HTTP_HOST']));
+			if (!strncmp(self::$_domain, 'www.', 4))
+			{
+				self::$_subdomain = self::$_domain;
+				self::$_domain = substr(self::$_domain, 4);
+			}
+			return self::$_domain;
+		}
+	}
+	
+	/**
+	 * Set session domain.
+	 * 
+	 * @return bool
+	 */
+	public static function setDomain($domain)
+	{
+		if (self::$_started)
+		{
+			return false;
+		}
+		else
+		{
+			self::$_domain = $domain;
+			self::$_subdomain = false;
+			return true;
+		}
+	}
+	
 	/**
 	 * Mark the current session as trusted for a given duration.
 	 * 
@@ -930,7 +974,7 @@ class Session
 	{
 		$lifetime = Config::get('session.lifetime');
 		$refresh = Config::get('session.refresh') ?: 300;
-		$domain = Config::get('session.domain') ?: (ini_get('session.cookie_domain') ?: preg_replace('/:\\d+$/', '', $_SERVER['HTTP_HOST']));
+		$domain = self::getDomain();
 		$path = Config::get('session.path') ?: ini_get('session.cookie_path');
 		return array($lifetime, $refresh, $domain, $path);
 	}
@@ -996,6 +1040,15 @@ class Session
 			$_COOKIE['rx_sesskey2'] = $_SESSION['RHYMIX']['keys'][$domain]['key2'];
 		}
 		
+		// Delete keys from subdomain.
+		if (self::$_subdomain && !isset($_SESSION['RHYMIX']['keys'][self::$_subdomain]['deleted']))
+		{
+			setcookie(session_name(), session_id(), $lifetime, $path, $domain, false, false);
+			setcookie(session_name(), 'deleted', time() - 86400, $path, self::$_subdomain, false, false);
+			setcookie('rx_sesskey1', 'deleted', time() - 86400, $path, self::$_subdomain, false, false);
+			setcookie('rx_sesskey2', 'deleted', time() - 86400, $path, self::$_subdomain, false, false);
+			$_SESSION['RHYMIX']['keys'][self::$_subdomain]['deleted'] = true;
+		}
 		return true;
 	}
 	
diff --git a/tests/unit/framework/SessionTest.php b/tests/unit/framework/SessionTest.php
index 0348ecb7a..749fb3246 100644
--- a/tests/unit/framework/SessionTest.php
+++ b/tests/unit/framework/SessionTest.php
@@ -48,9 +48,11 @@ class SessionTest extends \Codeception\TestCase\Test
 		$this->assertTrue(isset($_COOKIE['rx_sesskey1']));
 		$this->assertTrue(isset($_COOKIE['rx_sesskey2']));
 		$this->assertNotEmpty($_SESSION['RHYMIX']['secret']);
-		$this->assertEquals($_SESSION['RHYMIX']['keys']['www.rhymix.org']['key1'], $_COOKIE['rx_sesskey1']);
-		$this->assertEquals($_SESSION['RHYMIX']['keys']['www.rhymix.org']['key2'], $_COOKIE['rx_sesskey2']);
-		$this->assertEquals(0, $_SESSION['RHYMIX']['keys']['www.rhymix.org']['trusted']);
+		$this->assertEquals($_SESSION['RHYMIX']['keys']['rhymix.org']['key1'], $_COOKIE['rx_sesskey1']);
+		$this->assertEquals($_SESSION['RHYMIX']['keys']['rhymix.org']['key2'], $_COOKIE['rx_sesskey2']);
+		$this->assertEquals(0, $_SESSION['RHYMIX']['keys']['rhymix.org']['trusted']);
+		$this->assertFalse(isset($_SESSION['RHYMIX']['keys']['www.rhymix.org']['started']));
+		$this->assertTrue(isset($_SESSION['RHYMIX']['keys']['www.rhymix.org']['deleted']));
 		$session_secret = $_SESSION['RHYMIX']['secret'];
 		Rhymix\Framework\Session::close();
 		
@@ -90,7 +92,7 @@ class SessionTest extends \Codeception\TestCase\Test
 		
 		// Test initial transition from HTTP to HTTPS.
 		session_start();
-		unset($_SESSION['RHYMIX']['keys']['www.rhymix.org']['key2']);
+		unset($_SESSION['RHYMIX']['keys']['rhymix.org']['key2']);
 		unset($_COOKIE['rx_sesskey2']);
 		session_write_close();
 		$this->assertTrue(@Rhymix\Framework\Session::start());
@@ -139,17 +141,17 @@ class SessionTest extends \Codeception\TestCase\Test
 	{
 		@Rhymix\Framework\Session::start();
 		$session_secret = $_SESSION['RHYMIX']['secret'];
-		$key1 = $_SESSION['RHYMIX']['keys']['www.rhymix.org']['key1'];
-		$key2 = $_SESSION['RHYMIX']['keys']['www.rhymix.org']['key2'];
-		$_SESSION['RHYMIX']['keys']['www.rhymix.org']['key1_time'] = time() - 3600;
-		$_SESSION['RHYMIX']['keys']['www.rhymix.org']['key2_time'] = time() - 3600;
+		$key1 = $_SESSION['RHYMIX']['keys']['rhymix.org']['key1'];
+		$key2 = $_SESSION['RHYMIX']['keys']['rhymix.org']['key2'];
+		$_SESSION['RHYMIX']['keys']['rhymix.org']['key1_time'] = time() - 3600;
+		$_SESSION['RHYMIX']['keys']['rhymix.org']['key2_time'] = time() - 3600;
 		Rhymix\Framework\Session::close();
 		
 		@Rhymix\Framework\Session::start();
-		$this->assertNotEquals($key1, $_SESSION['RHYMIX']['keys']['www.rhymix.org']['key1']);
-		$this->assertNotEquals($key2, $_SESSION['RHYMIX']['keys']['www.rhymix.org']['key2']);
-		$this->assertEquals($key1, $_SESSION['RHYMIX']['keys']['www.rhymix.org']['key1_prev']);
-		$this->assertEquals($key2, $_SESSION['RHYMIX']['keys']['www.rhymix.org']['key2_prev']);
+		$this->assertNotEquals($key1, $_SESSION['RHYMIX']['keys']['rhymix.org']['key1']);
+		$this->assertNotEquals($key2, $_SESSION['RHYMIX']['keys']['rhymix.org']['key2']);
+		$this->assertEquals($key1, $_SESSION['RHYMIX']['keys']['rhymix.org']['key1_prev']);
+		$this->assertEquals($key2, $_SESSION['RHYMIX']['keys']['rhymix.org']['key2_prev']);
 		$this->assertEquals($session_secret, $_SESSION['RHYMIX']['secret']);
 		Rhymix\Framework\Session::close();
 	}
@@ -231,9 +233,9 @@ class SessionTest extends \Codeception\TestCase\Test
 	{
 		@Rhymix\Framework\Session::start();
 		
-		$_SESSION['RHYMIX']['keys']['www.rhymix.org']['trusted'] = 0;
+		$_SESSION['RHYMIX']['keys']['rhymix.org']['trusted'] = 0;
 		$this->assertFalse(Rhymix\Framework\Session::isTrusted());
-		$_SESSION['RHYMIX']['keys']['www.rhymix.org']['trusted'] = time() + 300;
+		$_SESSION['RHYMIX']['keys']['rhymix.org']['trusted'] = time() + 300;
 		$this->assertTrue(Rhymix\Framework\Session::isTrusted());
 		
 		Rhymix\Framework\Session::close();