diff --git a/changelog.d/12112.docker b/changelog.d/12112.docker
new file mode 100644
index 0000000000000000000000000000000000000000..b9e630653d249668e278b1a8a3dd1e76e86ad74c
--- /dev/null
+++ b/changelog.d/12112.docker
@@ -0,0 +1 @@
+Use Python 3.9 in Docker images by default.
\ No newline at end of file
diff --git a/docker/Dockerfile b/docker/Dockerfile
index e4c1c19b86a7ac7cc2592d534802e1362a88c619..a8bb9b0e7f7f931edb160ac9e2471a0d5971cb0d 100644
--- a/docker/Dockerfile
+++ b/docker/Dockerfile
@@ -11,10 +11,10 @@
 # There is an optional PYTHON_VERSION build argument which sets the
 # version of python to build against: for example:
 #
-#    DOCKER_BUILDKIT=1 docker build -f docker/Dockerfile --build-arg PYTHON_VERSION=3.9 .
+#    DOCKER_BUILDKIT=1 docker build -f docker/Dockerfile --build-arg PYTHON_VERSION=3.10 .
 #
 
-ARG PYTHON_VERSION=3.8
+ARG PYTHON_VERSION=3.9
 
 ###
 ### Stage 0: builder