diff --git a/CHANGES.rst b/CHANGES.rst
index 83560ec..99ece7f 100644
--- a/CHANGES.rst
+++ b/CHANGES.rst
@@ -2,6 +2,12 @@
  Changes
 =========
 
+5.1 (unreleased)
+================
+
+- Nothing changed yet.
+
+
 5.0 (2023-01-06)
 ================
 
diff --git a/setup.py b/setup.py
index 8a04141..e0099ce 100644
--- a/setup.py
+++ b/setup.py
@@ -30,7 +30,7 @@ def read(*rnames):
 ]
 
 setup(name='zope.authentication',
-      version='5.0',
+      version='5.1.dev0',
       author='Zope Foundation and Contributors',
       author_email='zope-dev@zope.org',
       description='Definition of authentication basics for the Zope Framework',