diff --git a/.bumpversion.cfg b/.bumpversion.cfg
index 577664a..e1f782d 100644
--- a/.bumpversion.cfg
+++ b/.bumpversion.cfg
@@ -1,5 +1,5 @@
 [bumpversion]
-current_version = 0.4.20
+current_version = 0.4.21
 commit = True
 tag = True
 
diff --git a/README.md b/README.md
index 604f55f..e8965d7 100644
--- a/README.md
+++ b/README.md
@@ -1,4 +1,4 @@
-# abp 0.4.20
+# abp 0.4.21
 
 Python port of Anders and Briegel' s [method](https://arxiv.org/abs/quant-ph/0504117) for fast simulation of Clifford circuits. You can read the full documentation [here](https://peteshadbolt.co.uk/abp/).
 
@@ -7,7 +7,7 @@ Python port of Anders and Briegel' s [method](https://arxiv.org/abs/quant-ph/050
 It's easiest to install with `pip`:
 
 ```shell
-$ pip install --user abp==0.4.20
+$ pip install --user abp==0.4.21
 ```
 
 Or clone and install in `develop` mode:
diff --git a/abp/static/index.html b/abp/static/index.html
index 36c66ed..6ee1bad 100644
--- a/abp/static/index.html
+++ b/abp/static/index.html
@@ -25,7 +25,7 @@
 <div id=node_info class=hidden> nothing </div>
 <div id=server_info class=hidden> </div>
 
-<div id=version>Version 0.4.20</div>
+<div id=version>Version 0.4.21</div>
 
 <div id=node_data class=hidden>
 <div id=node_name></div>
diff --git a/doc/conf.py b/doc/conf.py
index bce190c..fb55a7a 100644
--- a/doc/conf.py
+++ b/doc/conf.py
@@ -60,9 +60,9 @@ author = u'Pete Shadbolt'
 # built documents.
 #
 # The short X.Y version.
-version = '0.4.20'
+version = '0.4.21'
 # The full version, including alpha/beta/rc tags.
-release = '0.4.20'
+release = '0.4.21'
 
 # The language for content autogenerated by Sphinx. Refer to documentation
 # for a list of supported languages.
diff --git a/doc/index.rst b/doc/index.rst
index 3226081..9fbcb3c 100644
--- a/doc/index.rst
+++ b/doc/index.rst
@@ -26,7 +26,7 @@ You can install from ``pip``:
 
 .. code-block:: bash
 
-   $ pip install --user abp==0.4.20
+   $ pip install --user abp==0.4.21
 
 Alternatively, clone from the `github repo <https://github.com/peteshadbolt/abp>`_ and run ``setup.py``:
 
diff --git a/setup.py b/setup.py
index 76a4d68..27ad1fb 100755
--- a/setup.py
+++ b/setup.py
@@ -6,7 +6,7 @@ STATIC = glob("abp/static/*.*")+glob("abp/static/img/*.*")+glob("abp/static/scri
 
 setup(
     name = "abp",
-    version = "0.4.20",
+    version = "0.4.21",
     packages = ["abp", "abp.static"],
     test_suite = "tests",
     author = "Pete Shadbolt",