diff --git a/CHANGES.rst b/CHANGES.rst
index 04ddc9d0..824df243 100644
--- a/CHANGES.rst
+++ b/CHANGES.rst
@@ -2,6 +2,12 @@ Changelog of threedigrid-builder
 ================================
 
 
+1.21.4 (unreleased)
+-------------------
+
+- Nothing changed yet.
+
+
 1.21.3 (2024-12-17)
 -------------------
 
diff --git a/threedigrid_builder/__init__.py b/threedigrid_builder/__init__.py
index 627bcece..d6017964 100644
--- a/threedigrid_builder/__init__.py
+++ b/threedigrid_builder/__init__.py
@@ -2,5 +2,5 @@
 from .exceptions import *  # NOQA
 
 # fmt: off
-__version__ = '1.21.3'
+__version__ = '1.21.4.dev0'
 # fmt: on