diff --git a/HISTORY.rst b/HISTORY.rst
index 69d61fd..5cf3210 100644
--- a/HISTORY.rst
+++ b/HISTORY.rst
@@ -1,6 +1,12 @@
 History
 =======
 
+2.2.1 (unreleased)
+------------------
+
+- Nothing changed yet.
+
+
 2.2.0 (2023-11-07)
 ------------------
 
diff --git a/threedigrid/__init__.py b/threedigrid/__init__.py
index 0141830..af86ffc 100644
--- a/threedigrid/__init__.py
+++ b/threedigrid/__init__.py
@@ -1,3 +1,3 @@
 # Threedigrid version number is automatic updated with zest.releaser
 # the version number in setup.py is updated using the find_version()
-__version__ = "2.2.0"
+__version__ = "2.2.1.dev0"