diff --git a/socketio/asyncio_server.py b/socketio/asyncio_server.py
index 1610e5e..c3f62b9 100644
--- a/socketio/asyncio_server.py
+++ b/socketio/asyncio_server.py
@@ -259,7 +259,8 @@ class AsyncServer(server.Server):
         the user session, use the ``session`` context manager instead.
         """
         namespace = namespace or '/'
-        eio_session = await self.eio.get_session(sid)
+        eio_sid = self.manager.eio_sid_from_sid(sid, namespace)
+        eio_session = await self.eio.get_session(eio_sid)
         return eio_session.setdefault(namespace, {})
 
     async def save_session(self, sid, session, namespace=None):
@@ -271,7 +272,8 @@ class AsyncServer(server.Server):
                           the default namespace is used.
         """
         namespace = namespace or '/'
-        eio_session = await self.eio.get_session(sid)
+        eio_sid = self.manager.eio_sid_from_sid(sid, namespace)
+        eio_session = await self.eio.get_session(eio_sid)
         eio_session[namespace] = session
 
     def session(self, sid, namespace=None):
diff --git a/socketio/server.py b/socketio/server.py
index 18b2188..97be827 100644
--- a/socketio/server.py
+++ b/socketio/server.py
@@ -444,7 +444,8 @@ class Server(object):
         is used.
         """
         namespace = namespace or '/'
-        eio_session = self.eio.get_session(sid)
+        eio_sid = self.manager.eio_sid_from_sid(sid, namespace)
+        eio_session = self.eio.get_session(eio_sid)
         return eio_session.setdefault(namespace, {})
 
     def save_session(self, sid, session, namespace=None):
@@ -456,7 +457,8 @@ class Server(object):
                           the default namespace is used.
         """
         namespace = namespace or '/'
-        eio_session = self.eio.get_session(sid)
+        eio_sid = self.manager.eio_sid_from_sid(sid, namespace)
+        eio_session = self.eio.get_session(eio_sid)
         eio_session[namespace] = session
 
     def session(self, sid, namespace=None):
diff --git a/tests/asyncio/test_asyncio_server.py b/tests/asyncio/test_asyncio_server.py
index 254c944..932fcec 100644
--- a/tests/asyncio/test_asyncio_server.py
+++ b/tests/asyncio/test_asyncio_server.py
@@ -730,11 +730,13 @@ class TestAsyncServer(unittest.TestCase):
     def test_session(self, eio):
         fake_session = {}
 
-        async def fake_get_session(sid):
+        async def fake_get_session(eio_sid):
+            assert eio_sid == '123'
             return fake_session
 
-        async def fake_save_session(sid, session):
+        async def fake_save_session(eio_sid, session):
             global fake_session
+            assert eio_sid == '123'
             fake_session = session
 
         eio.return_value.send = AsyncMock()
@@ -744,17 +746,21 @@ class TestAsyncServer(unittest.TestCase):
 
         async def _test():
             await s._handle_eio_connect('123', 'environ')
-            await s.save_session('123', {'foo': 'bar'})
-            async with s.session('123') as session:
+            await s._handle_eio_message('123', '0')
+            await s._handle_eio_message('123', '0/ns')
+            sid = s.manager.sid_from_eio_sid('123', '/')
+            sid2 = s.manager.sid_from_eio_sid('123', '/ns')
+            await s.save_session(sid, {'foo': 'bar'})
+            async with s.session(sid) as session:
                 assert session == {'foo': 'bar'}
                 session['foo'] = 'baz'
                 session['bar'] = 'foo'
-            assert await s.get_session('123') == {'foo': 'baz', 'bar': 'foo'}
+            assert await s.get_session(sid) == {'foo': 'baz', 'bar': 'foo'}
             assert fake_session == {'/': {'foo': 'baz', 'bar': 'foo'}}
-            async with s.session('123', namespace='/ns') as session:
+            async with s.session(sid2, namespace='/ns') as session:
                 assert session == {}
                 session['a'] = 'b'
-            assert await s.get_session('123', namespace='/ns') == {'a': 'b'}
+            assert await s.get_session(sid2, namespace='/ns') == {'a': 'b'}
             assert fake_session == {
                 '/': {'foo': 'baz', 'bar': 'foo'},
                 '/ns': {'a': 'b'},
diff --git a/tests/common/test_server.py b/tests/common/test_server.py
index 0732bc3..e93c932 100644
--- a/tests/common/test_server.py
+++ b/tests/common/test_server.py
@@ -627,28 +627,34 @@ class TestServer(unittest.TestCase):
     def test_session(self, eio):
         fake_session = {}
 
-        def fake_get_session(sid):
+        def fake_get_session(eio_sid):
+            assert eio_sid == '123'
             return fake_session
 
-        def fake_save_session(sid, session):
+        def fake_save_session(eio_sid, session):
             global fake_session
+            assert eio_sid == '123'
             fake_session = session
 
         s = server.Server()
         s.eio.get_session = fake_get_session
         s.eio.save_session = fake_save_session
         s._handle_eio_connect('123', 'environ')
-        s.save_session('123', {'foo': 'bar'})
-        with s.session('123') as session:
+        s._handle_eio_message('123', '0')
+        s._handle_eio_message('123', '0/ns')
+        sid = s.manager.sid_from_eio_sid('123', '/')
+        sid2 = s.manager.sid_from_eio_sid('123', '/ns')
+        s.save_session(sid, {'foo': 'bar'})
+        with s.session(sid) as session:
             assert session == {'foo': 'bar'}
             session['foo'] = 'baz'
             session['bar'] = 'foo'
-        assert s.get_session('123') == {'foo': 'baz', 'bar': 'foo'}
+        assert s.get_session(sid) == {'foo': 'baz', 'bar': 'foo'}
         assert fake_session == {'/': {'foo': 'baz', 'bar': 'foo'}}
-        with s.session('123', namespace='/ns') as session:
+        with s.session(sid2, namespace='/ns') as session:
             assert session == {}
             session['a'] = 'b'
-        assert s.get_session('123', namespace='/ns') == {'a': 'b'}
+        assert s.get_session(sid2, namespace='/ns') == {'a': 'b'}
         assert fake_session == {
             '/': {'foo': 'baz', 'bar': 'foo'},
             '/ns': {'a': 'b'},