diff --git a/example/app.py b/example/app.py
index 86fc5133..a2732f5e 100755
--- a/example/app.py
+++ b/example/app.py
@@ -24,8 +24,7 @@ def background_thread():
         socketio.sleep(10)
         count += 1
         socketio.emit('my_response',
-                      {'data': 'Server generated event', 'count': count},
-                      namespace='/test')
+                      {'data': 'Server generated event', 'count': count})
 
 
 @app.route('/')
@@ -33,14 +32,14 @@ def index():
     return render_template('index.html', async_mode=socketio.async_mode)
 
 
-@socketio.on('my_event', namespace='/test')
+@socketio.on('my_event')
 def test_message(message):
     session['receive_count'] = session.get('receive_count', 0) + 1
     emit('my_response',
          {'data': message['data'], 'count': session['receive_count']})
 
 
-@socketio.on('my_broadcast_event', namespace='/test')
+@socketio.on('my_broadcast_event')
 def test_broadcast_message(message):
     session['receive_count'] = session.get('receive_count', 0) + 1
     emit('my_response',
@@ -48,7 +47,7 @@ def test_broadcast_message(message):
          broadcast=True)
 
 
-@socketio.on('join', namespace='/test')
+@socketio.on('join')
 def join(message):
     join_room(message['room'])
     session['receive_count'] = session.get('receive_count', 0) + 1
@@ -57,7 +56,7 @@ def join(message):
           'count': session['receive_count']})
 
 
-@socketio.on('leave', namespace='/test')
+@socketio.on('leave')
 def leave(message):
     leave_room(message['room'])
     session['receive_count'] = session.get('receive_count', 0) + 1
@@ -66,7 +65,7 @@ def leave(message):
           'count': session['receive_count']})
 
 
-@socketio.on('close_room', namespace='/test')
+@socketio.on('close_room')
 def close(message):
     session['receive_count'] = session.get('receive_count', 0) + 1
     emit('my_response', {'data': 'Room ' + message['room'] + ' is closing.',
@@ -75,7 +74,7 @@ def close(message):
     close_room(message['room'])
 
 
-@socketio.on('my_room_event', namespace='/test')
+@socketio.on('my_room_event')
 def send_room_message(message):
     session['receive_count'] = session.get('receive_count', 0) + 1
     emit('my_response',
@@ -83,7 +82,7 @@ def send_room_message(message):
          room=message['room'])
 
 
-@socketio.on('disconnect_request', namespace='/test')
+@socketio.on('disconnect_request')
 def disconnect_request():
     @copy_current_request_context
     def can_disconnect():
@@ -98,12 +97,12 @@ def can_disconnect():
          callback=can_disconnect)
 
 
-@socketio.on('my_ping', namespace='/test')
+@socketio.on('my_ping')
 def ping_pong():
     emit('my_pong')
 
 
-@socketio.on('connect', namespace='/test')
+@socketio.on('connect')
 def test_connect():
     global thread
     with thread_lock:
@@ -112,10 +111,10 @@ def test_connect():
     emit('my_response', {'data': 'Connected', 'count': 0})
 
 
-@socketio.on('disconnect', namespace='/test')
+@socketio.on('disconnect')
 def test_disconnect():
     print('Client disconnected', request.sid)
 
 
 if __name__ == '__main__':
-    socketio.run(app, debug=True)
+    socketio.run(app)
diff --git a/example/templates/index.html b/example/templates/index.html
index a2a6d4df..a338d0ca 100644
--- a/example/templates/index.html
+++ b/example/templates/index.html
@@ -2,21 +2,14 @@
 <html>
 <head>
     <title>Flask-SocketIO Test</title>
-    <script src="//code.jquery.com/jquery-1.12.4.min.js" integrity="sha256-ZosEbRLbNQzLpnKIkEdrPv7lOy9C27hHQ+Xp8a4MxAQ=" crossorigin="anonymous"></script>
-    <script src="//cdnjs.cloudflare.com/ajax/libs/socket.io/2.2.0/socket.io.js" integrity="sha256-yr4fRk/GU1ehYJPAs8P4JlTgu0Hdsp4ZKrx8bDEDC3I=" crossorigin="anonymous"></script>
+    <script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.5.1/jquery.min.js" integrity="sha512-bLT0Qm9VnAYZDflyKcBaQ2gg0hSYNQrJ8RilYldYQ1FxQYoCLtUjuuRuZo+fjqhx/qtq/1itJ0C2ejDxltZVFg==" crossorigin="anonymous"></script>
+    <script src="https://cdnjs.cloudflare.com/ajax/libs/socket.io/3.0.4/socket.io.js" integrity="sha512-aMGMvNYu8Ue4G+fHa359jcPb1u+ytAF+P2SCb+PxrjCdO3n3ZTxJ30zuH39rimUggmTwmh2u7wvQsDTHESnmfQ==" crossorigin="anonymous"></script>
     <script type="text/javascript" charset="utf-8">
         $(document).ready(function() {
-            // Use a "/test" namespace.
-            // An application can open a connection on multiple namespaces, and
-            // Socket.IO will multiplex all those connections on a single
-            // physical channel. If you don't care about multiple channels, you
-            // can set the namespace to an empty string.
-            namespace = '/test';
-
             // Connect to the Socket.IO server.
             // The connection URL has the following format, relative to the current page:
             //     http[s]://<domain>:<port>[/<namespace>]
-            var socket = io(namespace);
+            var socket = io();
 
             // Event handler for new connections.
             // The callback function is invoked when a connection with the
diff --git a/flask_socketio/__init__.py b/flask_socketio/__init__.py
index 8ecf0b47..63a2cb60 100644
--- a/flask_socketio/__init__.py
+++ b/flask_socketio/__init__.py
@@ -686,18 +686,19 @@ def test_client(self, app, namespace=None, query_string=None,
                                   flask_test_client=flask_test_client)
 
     def _handle_event(self, handler, message, namespace, sid, *args):
-        if sid not in self.server.environ:
+        eio_sid = self.server.manager.eio_sid_from_sid(sid, namespace)
+        environ = self.server.get_environ(sid, namespace=namespace)
+        if not environ:
             # we don't have record of this client, ignore this event
             return '', 400
-        app = self.server.environ[sid]['flask.app']
-        with app.request_context(self.server.environ[sid]):
+        app = environ['flask.app']
+        with app.request_context(environ):
             if self.manage_session:
                 # manage a separate session for this client's Socket.IO events
                 # created as a copy of the regular user session
-                if 'saved_session' not in self.server.environ[sid]:
-                    self.server.environ[sid]['saved_session'] = \
-                        _ManagedSession(flask.session)
-                session_obj = self.server.environ[sid]['saved_session']
+                if 'saved_session' not in environ:
+                    environ['saved_session'] = _ManagedSession(flask.session)
+                session_obj = environ['saved_session']
             else:
                 # let Flask handle the user session
                 # for cookie based sessions, this effectively freezes the
diff --git a/flask_socketio/test_client.py b/flask_socketio/test_client.py
index 153eba7d..1148d075 100644
--- a/flask_socketio/test_client.py
+++ b/flask_socketio/test_client.py
@@ -28,36 +28,38 @@ class SocketIOTestClient(object):
 
     def __init__(self, app, socketio, namespace=None, query_string=None,
                  headers=None, flask_test_client=None):
-        def _mock_send_packet(sid, pkt):
+        def _mock_send_packet(eio_sid, pkt):
             if pkt.packet_type == packet.EVENT or \
                     pkt.packet_type == packet.BINARY_EVENT:
-                if sid not in self.queue:
-                    self.queue[sid] = []
+                if eio_sid not in self.queue:
+                    self.queue[eio_sid] = []
                 if pkt.data[0] == 'message' or pkt.data[0] == 'json':
-                    self.queue[sid].append({'name': pkt.data[0],
-                                            'args': pkt.data[1],
-                                            'namespace': pkt.namespace or '/'})
+                    self.queue[eio_sid].append({
+                        'name': pkt.data[0],
+                        'args': pkt.data[1],
+                        'namespace': pkt.namespace or '/'})
                 else:
-                    self.queue[sid].append({'name': pkt.data[0],
-                                            'args': pkt.data[1:],
-                                            'namespace': pkt.namespace or '/'})
+                    self.queue[eio_sid].append({
+                        'name': pkt.data[0],
+                        'args': pkt.data[1:],
+                        'namespace': pkt.namespace or '/'})
             elif pkt.packet_type == packet.ACK or \
                     pkt.packet_type == packet.BINARY_ACK:
-                self.acks[sid] = {'args': pkt.data,
-                                  'namespace': pkt.namespace or '/'}
-            elif pkt.packet_type in [packet.DISCONNECT, packet.ERROR]:
+                self.acks[eio_sid] = {'args': pkt.data,
+                                      'namespace': pkt.namespace or '/'}
+            elif pkt.packet_type in [packet.DISCONNECT, packet.CONNECT_ERROR]:
                 self.connected[pkt.namespace or '/'] = False
 
         self.app = app
         self.flask_test_client = flask_test_client
-        self.sid = uuid.uuid4().hex
-        self.queue[self.sid] = []
-        self.acks[self.sid] = None
+        self.eio_sid = uuid.uuid4().hex
+        self.acks[self.eio_sid] = None
+        self.queue[self.eio_sid] = []
         self.callback_counter = 0
         self.socketio = socketio
         self.connected = {}
         socketio.server._send_packet = _mock_send_packet
-        socketio.server.environ[self.sid] = {}
+        socketio.server.environ[self.eio_sid] = {}
         socketio.server.async_handlers = False      # easier to test when
         socketio.server.eio.async_handlers = False  # events are sync
         if isinstance(socketio.server.manager, PubSubManager):
@@ -91,6 +93,7 @@ def connect(self, namespace=None, query_string=None, headers=None):
         is when the application accepts multiple namespace connections.
         """
         url = '/socket.io'
+        namespace = namespace or '/'
         if query_string:
             if query_string[0] != '?':
                 query_string = '?' + query_string
@@ -100,16 +103,15 @@ def connect(self, namespace=None, query_string=None, headers=None):
         if self.flask_test_client:
             # inject cookies from Flask
             self.flask_test_client.cookie_jar.inject_wsgi(environ)
-        ret = self.socketio.server._handle_eio_connect(self.sid, environ)
-        if ret is None or ret is True:
-            self.connected['/'] = True
-        if namespace is not None and namespace != '/':
-            pkt = packet.Packet(packet.CONNECT, namespace=namespace)
-            with self.app.app_context():
-                ret = self.socketio.server._handle_eio_message(self.sid,
-                                                               pkt.encode())
-            if ret is None or ret is True:
-                self.connected[namespace] = True
+        self.socketio.server._handle_eio_connect(self.eio_sid, environ)
+        pkt = packet.Packet(packet.CONNECT, namespace=namespace)
+        with self.app.app_context():
+            ret = self.socketio.server._handle_eio_message(self.eio_sid,
+                                                           pkt.encode())
+        sid = self.socketio.server.manager.sid_from_eio_sid(self.eio_sid,
+                                                            namespace)
+        if sid:
+            self.connected[namespace] = True
 
     def disconnect(self, namespace=None):
         """Disconnect the client.
@@ -121,7 +123,8 @@ def disconnect(self, namespace=None):
             raise RuntimeError('not connected')
         pkt = packet.Packet(packet.DISCONNECT, namespace=namespace)
         with self.app.app_context():
-            self.socketio.server._handle_eio_message(self.sid, pkt.encode())
+            self.socketio.server._handle_eio_message(self.eio_sid,
+                                                     pkt.encode())
         del self.connected[namespace or '/']
 
     def emit(self, event, *args, **kwargs):
@@ -153,10 +156,12 @@ def emit(self, event, *args, **kwargs):
             encoded_pkt = pkt.encode()
             if isinstance(encoded_pkt, list):
                 for epkt in encoded_pkt:
-                    self.socketio.server._handle_eio_message(self.sid, epkt)
+                    self.socketio.server._handle_eio_message(self.eio_sid,
+                                                             epkt)
             else:
-                self.socketio.server._handle_eio_message(self.sid, encoded_pkt)
-        ack = self.acks.pop(self.sid, None)
+                self.socketio.server._handle_eio_message(self.eio_sid,
+                                                         encoded_pkt)
+        ack = self.acks.pop(self.eio_sid, None)
         if ack is not None:
             return ack['args'][0] if len(ack['args']) == 1 \
                 else ack['args']
@@ -197,8 +202,8 @@ def get_received(self, namespace=None):
         if not self.is_connected(namespace):
             raise RuntimeError('not connected')
         namespace = namespace or '/'
-        r = [pkt for pkt in self.queue[self.sid]
+        r = [pkt for pkt in self.queue[self.eio_sid]
              if pkt['namespace'] == namespace]
-        self.queue[self.sid] = [pkt for pkt in self.queue[self.sid]
-                                if pkt not in r]
+        self.queue[self.eio_sid] = [
+            pkt for pkt in self.queue[self.eio_sid] if pkt not in r]
         return r
diff --git a/setup.py b/setup.py
index caa813e2..f5892443 100755
--- a/setup.py
+++ b/setup.py
@@ -26,7 +26,7 @@
     platforms='any',
     install_requires=[
         'Flask>=0.9',
-        'python-socketio>=4.3.0,<5'
+        'python-socketio>=5.0.2'
     ],
     tests_require=[
         'coverage'
@@ -38,7 +38,6 @@
         'License :: OSI Approved :: MIT License',
         'Operating System :: OS Independent',
         'Programming Language :: Python',
-        'Programming Language :: Python :: 2',
         'Programming Language :: Python :: 3',
         'Topic :: Internet :: WWW/HTTP :: Dynamic Content',
         'Topic :: Software Development :: Libraries :: Python Modules'
diff --git a/test_socketio.py b/test_socketio.py
index 356ab0fa..6ea761a2 100755
--- a/test_socketio.py
+++ b/test_socketio.py
@@ -264,7 +264,7 @@ def test_connect(self):
         client2 = socketio.test_client(app)
         self.assertTrue(client.is_connected())
         self.assertTrue(client2.is_connected())
-        self.assertNotEqual(client.sid, client2.sid)
+        self.assertNotEqual(client.eio_sid, client2.eio_sid)
         received = client.get_received()
         self.assertEqual(len(received), 3)
         self.assertEqual(received[0]['args'], 'connected')
@@ -443,11 +443,13 @@ def test_session(self):
         client = socketio.test_client(app, flask_test_client=flask_client)
         client.get_received()
         client.send('echo this message back')
-        self.assertEqual(socketio.server.environ[client.sid]['saved_session'],
-                         {'foo': 'bar'})
+        self.assertEqual(
+            socketio.server.environ[client.eio_sid]['saved_session'],
+            {'foo': 'bar'})
         client.send('test session')
-        self.assertEqual(socketio.server.environ[client.sid]['saved_session'],
-                         {'a': 'b', 'foo': 'bar'})
+        self.assertEqual(
+            socketio.server.environ[client.eio_sid]['saved_session'],
+            {'a': 'b', 'foo': 'bar'})
 
     def test_room(self):
         client1 = socketio.test_client(app)
