diff --git a/matemat/webserver/httpd.py b/matemat/webserver/httpd.py
index 2f3f3cb..5c75520 100644
--- a/matemat/webserver/httpd.py
+++ b/matemat/webserver/httpd.py
@@ -175,12 +175,13 @@ class HttpHandler(BaseHTTPRequestHandler):
         :param args: Arguments sent with the request.  This includes GET and POST arguments, where the POST arguments
                      take precedence.
         """
-        # Start or resume a session; report an error on session timeout
+        # Start or resume a session; redirect to / on session timeout
         try:
             session_id, timeout = self._start_session()
         except TimeoutError:
-            self.send_error(599, 'Session Timed Out', 'Session Timed Out.')
+            self.send_response(302)
             self.send_header('Set-Cookie', 'matemat_session_id=; expires=Thu, 01 Jan 1970 00:00:00 GMT')
+            self.send_header('Location', '/')
             self.end_headers()
             return
         self.session_id: str = session_id
diff --git a/matemat/webserver/test/abstract_httpd_test.py b/matemat/webserver/test/abstract_httpd_test.py
index a931628..eda18dd 100644
--- a/matemat/webserver/test/abstract_httpd_test.py
+++ b/matemat/webserver/test/abstract_httpd_test.py
@@ -39,7 +39,7 @@ class HttpResponse:
 
     def __finalize(self):
         self.parse_phase = 'done'
-        self.pagelet = self.headers['X-Test-Pagelet']
+        self.pagelet = self.headers.get('X-Test-Pagelet', None)
 
     def parse(self, fragment: bytes) -> None:
         """
diff --git a/matemat/webserver/test/test_session.py b/matemat/webserver/test/test_session.py
index 6697da3..b8e21cf 100644
--- a/matemat/webserver/test/test_session.py
+++ b/matemat/webserver/test/test_session.py
@@ -68,7 +68,7 @@ class TestSession(AbstractHttpdTest):
 
         # Send a mock GET request for '/just/testing/sessions' with a matemat session cookie
         self.client_sock.set_request(
-            f'GET /just/testing/sessions HTTP/1.1\r\nCookie: matemat_session_id={session_id}\r\n'.encode('utf-8'))
+            f'GET /just/testing/sessions HTTP/1.1\r\nCookie: matemat_session_id={session_id}\r\n\r\n'.encode('utf-8'))
         # Trigger request handling
         handler = HttpHandler(self.client_sock, ('::1', 45678), self.server)
         # Fetch the parsed response
@@ -98,3 +98,63 @@ class TestSession(AbstractHttpdTest):
         # Make sure the session exists on the server
         self.assertIn('test', handler.session_vars)
         self.assertEqual('hello, world!', handler.session_vars['test'])
+
+    def test_unknown_session_id(self):
+        # Unknown session ID
+        session_id: str = 'theserverdoesnotknowthisid'
+        refdate: datetime = datetime.utcnow() + timedelta(seconds=3500)
+        # Send a mock GET request for '/just/testing/sessions' with a session cookie not known to the server
+        self.client_sock.set_request(
+            f'GET /just/testing/sessions HTTP/1.1\r\nCookie: matemat_session_id={session_id}\r\n\r\n'.encode('utf-8'))
+        # Trigger request handling
+        handler = HttpHandler(self.client_sock, ('::1', 45678), self.server)
+        # Fetch the parsed response
+        packet = self.client_sock.get_response()
+        # Make sure a full HTTP response was parsed
+        self.assertEqual('done', packet.parse_phase)
+        # Make sure the request was served by the test pagelet
+        self.assertEqual('session_test_pagelet', packet.pagelet)
+        self.assertEqual(200, packet.statuscode)
+
+        server_session_id: str = list(handler.server.session_vars.keys())[0]
+        self.assertNotEqual(session_id, server_session_id)
+        # Make sure a cookie was set - assuming that only one was set
+        self.assertIn('Set-Cookie', packet.headers)
+        # Split into the cookie itself
+        cookie, expiry = packet.headers['Set-Cookie'].split(';')
+        cookie: str = cookie.strip()
+        expiry: str = expiry.strip()
+        # Make sure the 'matemat_session_id' cookie was set to the session ID string
+        self.assertEqual(f'matemat_session_id={server_session_id}', cookie)
+        # Make sure the session expires in about one hour
+        self.assertTrue(expiry.startswith('expires='))
+        _, expdatestr = expiry.split('=', 1)
+        expdate = datetime.strptime(expdatestr, '%a, %d %b %Y %H:%M:%S GMT')
+        self.assertTrue(expdate > refdate)
+        # Make sure the session exists on the server
+        self.assertIn('test', handler.session_vars)
+        self.assertEqual('hello, world!', handler.session_vars['test'])
+
+    def test_session_expired(self):
+        # Test session expiry date
+        refdate: datetime = datetime.utcnow() - timedelta(hours=1)
+        # Session ID for testing
+        session_id: str = 'testsessionid'
+        # Insert test session
+        self.server.session_vars[session_id] = refdate, {'test': 'bar'}
+
+        # Send a mock GET request for '/just/testing/sessions' with a matemat session cookie
+        self.client_sock.set_request(
+            f'GET /just/testing/sessions HTTP/1.1\r\nCookie: matemat_session_id={session_id}\r\n\r\n'.encode('utf-8'))
+        # Trigger request handling
+        handler = HttpHandler(self.client_sock, ('::1', 45678), self.server)
+        # Fetch the parsed response
+        packet = self.client_sock.get_response()
+        # Make sure a full HTTP response was parsed
+        self.assertEqual('done', packet.parse_phase)
+        # Make sure the server redirects to /
+        self.assertEqual(302, packet.statuscode)
+        self.assertIn('Location', packet.headers)
+        self.assertEqual('/', packet.headers['Location'])
+        # Make sure the session was terminated
+        self.assertNotIn(session_id, self.server.session_vars)