diff --git a/CHANGES.rst b/CHANGES.rst
index f748070..c4c685b 100644
--- a/CHANGES.rst
+++ b/CHANGES.rst
@@ -2,6 +2,12 @@
  Changes
 =========
 
+4.1 (unreleased)
+================
+
+- Nothing changed yet.
+
+
 4.0 (2023-11-13)
 ================
 
diff --git a/setup.py b/setup.py
index e323890..a105f06 100644
--- a/setup.py
+++ b/setup.py
@@ -17,7 +17,7 @@
 from setuptools import setup
 
 
-version = '4.0'
+version = '4.1.dev0'
 here = os.path.abspath(os.path.dirname(__file__))