diff --git a/docs/changelog.rst b/docs/changelog.rst
index 653e7971..6aa1b01a 100644
--- a/docs/changelog.rst
+++ b/docs/changelog.rst
@@ -18,6 +18,10 @@ To avail of fixes in an unreleased version, please download a ZIP file
 `directly from GitHub <https://github.com/mitogen-hq/mitogen/>`_.
 
 
+In progress (unreleased)
+------------------------
+
+
 v0.3.20 (2025-01-07)
 --------------------
 
diff --git a/mitogen/__init__.py b/mitogen/__init__.py
index 08a3bc58..0a34c21b 100644
--- a/mitogen/__init__.py
+++ b/mitogen/__init__.py
@@ -35,7 +35,7 @@ be expected. On the slave, it is built dynamically during startup.
 
 
 #: Library version as a tuple.
-__version__ = (0, 3, 20)
+__version__ = (0, 3, 21, 'dev')
 
 
 #: This is :data:`False` in slave contexts. Previously it was used to prevent