diff --git a/_metadata.py b/_metadata.py
index 5444bf15..2ad24c3a 100644
--- a/_metadata.py
+++ b/_metadata.py
@@ -1,2 +1,2 @@
-__extension_version__ = "0.3.0"
+__extension_version__ = "0.4.0"
 __extension_name__ = "pytket-qir"
diff --git a/docs/changelog.rst b/docs/changelog.rst
index 34d88948..0ec0944a 100644
--- a/docs/changelog.rst
+++ b/docs/changelog.rst
@@ -1,6 +1,11 @@
 Changelog
 ~~~~~~~~~
 
+0.4.0 (October 2023)
+--------------------
+
+* Updated pytket version requirement to 1.21.
+
 0.3.0 (September 2023)
 ----------------------
 * update pytket version to 1.20
diff --git a/setup.py b/setup.py
index 09d99746..c421500d 100644
--- a/setup.py
+++ b/setup.py
@@ -45,7 +45,7 @@
     packages=find_namespace_packages(include=["pytket.*"]),
     include_package_data=True,
     install_requires=[
-        "pytket ~= 1.20",
+        "pytket ~= 1.21",
         "pyqir == 0.8.2",
         "pyqir-generator == 0.7.0",
         "pyqir-evaluator == 0.7.0",