diff --git a/CHANGES.rst b/CHANGES.rst
index 1ca916c0ff..11082ca8b1 100644
--- a/CHANGES.rst
+++ b/CHANGES.rst
@@ -7,6 +7,12 @@ The change log for the previous version, Zope 2.13, is at
 https://zope.readthedocs.io/en/2.13/CHANGES.html
 
 
+4.5.1 (unreleased)
+------------------
+
+- Nothing changed yet.
+
+
 4.5 (2020-07-09)
 ----------------
 
diff --git a/setup.py b/setup.py
index 7d8ca638f2..079256fa06 100644
--- a/setup.py
+++ b/setup.py
@@ -29,7 +29,7 @@ def _read_file(filename):
 README = _read_file('README.rst')
 CHANGES = _read_file('CHANGES.rst')
 
-version = '4.5'
+version = '4.5.1.dev0'
 
 
 setup(