diff --git a/CHANGES.rst b/CHANGES.rst
index ffafe31..f2eef10 100644
--- a/CHANGES.rst
+++ b/CHANGES.rst
@@ -3,6 +3,12 @@
  Changes
 =========
 
+4.3.1 (unreleased)
+==================
+
+- Nothing changed yet.
+
+
 4.3.0 (2023-05-05)
 ==================
 
diff --git a/setup.py b/setup.py
index 0b768a9..e270db5 100755
--- a/setup.py
+++ b/setup.py
@@ -1,7 +1,7 @@
 import codecs
 from setuptools import setup, find_packages
 
-version = '4.3.0'
+version = '4.3.1.dev0'
 
 entry_points = {
     'console_scripts': [