diff --git a/CHANGES.rst b/CHANGES.rst
index e387cb6d67..9809e0b9c6 100644
--- a/CHANGES.rst
+++ b/CHANGES.rst
@@ -7,6 +7,10 @@ since the branch point at Zope 4.1.2.
 The change log for the previous version, Zope 4, is at
 https://github.com/zopefoundation/Zope/blob/4.x/CHANGES.rst
 
+5.9.1 (unreleased)
+------------------
+
+
 5.9 (2023-11-24)
 ----------------
 
diff --git a/requirements-full.txt b/requirements-full.txt
index 7180538935..c88cf0c9f7 100644
--- a/requirements-full.txt
+++ b/requirements-full.txt
@@ -1,4 +1,4 @@
-Zope==5.9
+-e git+https://github.com/zopefoundation/Zope.git@master#egg=Zope
 AccessControl==6.3
 Acquisition==5.1
 AuthEncoding==5.0
diff --git a/setup.py b/setup.py
index 928953d9d5..30259ebe71 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 = '5.9'
+version = '5.9.1.dev0'
 
 setup(
     name='Zope',
diff --git a/versions-prod.cfg b/versions-prod.cfg
index ee8e7c4059..b5bc1d1823 100644
--- a/versions-prod.cfg
+++ b/versions-prod.cfg
@@ -2,7 +2,7 @@
 # Version pins for required and commonly used dependencies.
 
 [versions]
-Zope = 5.9
+Zope =
 Zope2 = 4.0
 AccessControl = 6.3
 Acquisition = 5.1