diff --git a/CHANGES.rst b/CHANGES.rst
index 0e0023b..0b858f2 100644
--- a/CHANGES.rst
+++ b/CHANGES.rst
@@ -2,6 +2,12 @@
  Changes
 =========
 
+5.1 (unreleased)
+================
+
+- Nothing changed yet.
+
+
 5.0 (2023-02-24)
 ================
 
diff --git a/setup.py b/setup.py
index bc4cc6a..e07cbd6 100644
--- a/setup.py
+++ b/setup.py
@@ -31,7 +31,7 @@ def read(*rnames):
 
 setup(
     name='zope.securitypolicy',
-    version='5.0',
+    version='5.1.dev0',
     author='Zope Foundation and Contributors',
     author_email='zope-dev@zope.dev',
     description='Default security policy for Zope3',