diff --git a/socketIO_client/transports.py b/socketIO_client/transports.py
index f4b4a7c..c2ca31b 100644
--- a/socketIO_client/transports.py
+++ b/socketIO_client/transports.py
@@ -129,7 +129,7 @@ class WebsocketTransport(AbstractTransport):
                     proxy_url_pack.username, proxy_url_pack.password)
         if http_session.verify:
             if http_session.cert:  # Specify certificate path on disk
-                if isinstance(http_session.cert, basestring):
+                if isinstance(http_session.cert, str):
                     kw['ca_certs'] = http_session.cert
                 else:
                     kw['ca_certs'] = http_session.cert[0]