diff --git a/README.rst b/README.rst
index cc052e3..83ea1e7 100644
--- a/README.rst
+++ b/README.rst
@@ -21,7 +21,7 @@ is to use the same version of this package for the client and the server. If you
 using this package with a different client or server, then you must ensure the
 versions are compatible.
 
-The version compatiblity chart below maps versions of this package to versions
+The version compatibility chart below maps versions of this package to versions
 of the JavaScript reference implementation and the versions of the Socket.IO and
 Engine.IO protocols.
 
diff --git a/socketio/base_manager.py b/socketio/base_manager.py
index 58d4faa..24cd288 100644
--- a/socketio/base_manager.py
+++ b/socketio/base_manager.py
@@ -62,6 +62,10 @@ class BaseManager(object):
         if namespace in self.rooms:
             return self.rooms[namespace][None].inverse.get(eio_sid)
 
+    def eio_sid_from_sid(self, sid, namespace):
+        if namespace in self.rooms:
+            return self.rooms[namespace][None].get(sid)
+
     def can_disconnect(self, sid, namespace):
         return self.is_connected(sid, namespace)
 
diff --git a/tests/common/test_base_manager.py b/tests/common/test_base_manager.py
index 9518a46..af949ce 100644
--- a/tests/common/test_base_manager.py
+++ b/tests/common/test_base_manager.py
@@ -28,6 +28,11 @@ class TestBaseManager(unittest.TestCase):
         assert dict(self.bm.rooms['/foo'][None]) == {sid: '123'}
         assert dict(self.bm.rooms['/foo'][sid]) == {sid: '123'}
         assert self.bm.sid_from_eio_sid('123', '/foo') == sid
+        assert self.bm.sid_from_eio_sid('1234', '/foo') is None
+        assert self.bm.sid_from_eio_sid('123', '/bar') is None
+        assert self.bm.eio_sid_from_sid(sid, '/foo') == '123'
+        assert self.bm.eio_sid_from_sid('x', '/foo') is None
+        assert self.bm.eio_sid_from_sid(sid, '/bar') is None
 
     def test_pre_disconnect(self):
         sid1 = self.bm.connect('123', '/foo')