diff --git a/CHANGES.rst b/CHANGES.rst
index a5d5c82..fd92408 100644
--- a/CHANGES.rst
+++ b/CHANGES.rst
@@ -2,6 +2,12 @@
  Changes
 =========
 
+5.2.1 (unreleased)
+==================
+
+- Nothing changed yet.
+
+
 5.2.0 (2022-04-06)
 ==================
 
diff --git a/setup.py b/setup.py
index 57f3797..1806dc3 100644
--- a/setup.py
+++ b/setup.py
@@ -73,7 +73,7 @@ def _unavailable(self, e):
 
 
 setup(name='zope.index',
-      version='5.2.0',
+      version='5.2.1.dev0',
       url='https://github.com/zopefoundation/zope.index',
       license='ZPL 2.1',
       author='Zope Foundation and Contributors',