diff --git a/CHANGES.rst b/CHANGES.rst
index 7c13571..0cda315 100644
--- a/CHANGES.rst
+++ b/CHANGES.rst
@@ -2,6 +2,12 @@
  Changes
 =========
 
+5.1 (unreleased)
+================
+
+- Nothing changed yet.
+
+
 5.0 (2023-03-27)
 ================
 
diff --git a/setup.py b/setup.py
index 4e1d063..646df57 100644
--- a/setup.py
+++ b/setup.py
@@ -33,7 +33,7 @@ def read(*rnames):
 
 setup(
     name='zope.ptresource',
-    version='5.0',
+    version='5.1.dev0',
     url='https://github.com/zopefoundation/zope.ptresource/',
     project_urls={
         'Issue Tracker': ('https://github.com/zopefoundation/'