diff --git a/CHANGES.rst b/CHANGES.rst
index c795260..b873546 100644
--- a/CHANGES.rst
+++ b/CHANGES.rst
@@ -2,6 +2,12 @@
  Changes
 =========
 
+4.0.1 (unreleased)
+==================
+
+- Nothing changed yet.
+
+
 4.0.0 (2023-10-24)
 ==================
 
diff --git a/setup.py b/setup.py
index f7a7f6a..1a8bc07 100755
--- a/setup.py
+++ b/setup.py
@@ -4,7 +4,7 @@
 from setuptools import setup, find_packages
 
 
-version = '4.0.0'
+version = '4.0.1.dev0'
 
 entry_points = {
 }