diff --git a/setup.cfg b/setup.cfg
index 0c12541..291dafe 100644
--- a/setup.cfg
+++ b/setup.cfg
@@ -1,6 +1,6 @@
 [metadata]
 name = python-engineio
-version = 4.3.0
+version = 4.3.1.dev0
 author = Miguel Grinberg
 author_email = miguel.grinberg@gmail.com
 description = Engine.IO server and client for Python