diff --git a/.circleci/config.yml b/.circleci/config.yml
index e4fd5ffa6b..98c217dd1d 100644
--- a/.circleci/config.yml
+++ b/.circleci/config.yml
@@ -4,7 +4,7 @@ jobs:
     machine: true
     steps:
       - checkout
-      - run: docker build -f docker/Dockerfile --label gitsha1=${CIRCLE_SHA1} -t matrixdotorg/synapse:${CIRCLE_TAG} -t matrixdotorg/synapse:${CIRCLE_TAG}-py3 --build-arg PYTHON_VERSION=3.6 .
+      - run: docker build -f docker/Dockerfile --label gitsha1=${CIRCLE_SHA1} -t matrixdotorg/synapse:${CIRCLE_TAG} -t matrixdotorg/synapse:${CIRCLE_TAG}-py3 .
       - run: docker login --username $DOCKER_HUB_USERNAME --password $DOCKER_HUB_PASSWORD
       - run: docker push matrixdotorg/synapse:${CIRCLE_TAG}
       - run: docker push matrixdotorg/synapse:${CIRCLE_TAG}-py3
@@ -12,7 +12,7 @@ jobs:
     machine: true
     steps:
       - checkout
-      - run: docker build -f docker/Dockerfile --label gitsha1=${CIRCLE_SHA1} -t matrixdotorg/synapse:latest -t matrixdotorg/synapse:latest-py3 --build-arg PYTHON_VERSION=3.6 .
+      - run: docker build -f docker/Dockerfile --label gitsha1=${CIRCLE_SHA1} -t matrixdotorg/synapse:latest -t matrixdotorg/synapse:latest-py3 .
       - run: docker login --username $DOCKER_HUB_USERNAME --password $DOCKER_HUB_PASSWORD
       - run: docker push matrixdotorg/synapse:latest
       - run: docker push matrixdotorg/synapse:latest-py3
diff --git a/changelog.d/5546.feature b/changelog.d/5546.feature
new file mode 100644
index 0000000000..16952b62fc
--- /dev/null
+++ b/changelog.d/5546.feature
@@ -0,0 +1 @@
+Update docker image to use Python 3.7.
diff --git a/docker/Dockerfile b/docker/Dockerfile
index 24921eb098..0939cadf39 100644
--- a/docker/Dockerfile
+++ b/docker/Dockerfile
@@ -11,7 +11,7 @@
 #    docker build -f docker/Dockerfile --build-arg PYTHON_VERSION=3.6 .
 #
 
-ARG PYTHON_VERSION=2
+ARG PYTHON_VERSION=3.7
 
 ###
 ### Stage 0: builder