diff --git a/changelog.d/9685.misc b/changelog.d/9685.misc
new file mode 100644
index 0000000000..0506d8af0c
--- /dev/null
+++ b/changelog.d/9685.misc
@@ -0,0 +1 @@
+Update `scripts-dev/complement.sh` to use a local checkout of Complement, allow running a subset of tests and have it use Synapse's Complement test blacklist.
\ No newline at end of file
diff --git a/scripts-dev/complement.sh b/scripts-dev/complement.sh
index 3cde53f5c0..31cc20a826 100755
--- a/scripts-dev/complement.sh
+++ b/scripts-dev/complement.sh
@@ -1,22 +1,49 @@
-#! /bin/bash -eu
+#!/usr/bin/env bash
 # This script is designed for developers who want to test their code
 # against Complement.
 #
 # It makes a Synapse image which represents the current checkout,
-# then downloads Complement and runs it with that image.
+# builds a synapse-complement image on top, then runs tests with it.
+#
+# By default the script will fetch the latest Complement master branch and
+# run tests with that. This can be overridden to use a custom Complement
+# checkout by setting the COMPLEMENT_DIR environment variable to the
+# filepath of a local Complement checkout.
+#
+# A regular expression of test method names can be supplied as the first
+# argument to the script. Complement will then only run those tests. If
+# no regex is supplied, all tests are run. For example;
+#
+# ./complement.sh "TestOutboundFederation(Profile|Send)"
+#
 
+# Exit if a line returns a non-zero exit code
+set -e
+
+# Change to the repository root
 cd "$(dirname $0)/.."
 
+# Check for a user-specified Complement checkout
+if [[ -z "$COMPLEMENT_DIR" ]]; then
+  echo "COMPLEMENT_DIR not set. Fetching the latest Complement checkout..."
+  wget -Nq https://github.com/matrix-org/complement/archive/master.tar.gz
+  tar -xzf master.tar.gz
+  COMPLEMENT_DIR=complement-master
+  echo "Checkout available at 'complement-master'"
+fi
+
 # Build the base Synapse image from the local checkout
-docker build -t matrixdotorg/synapse:latest -f docker/Dockerfile .
+docker build -t matrixdotorg/synapse -f docker/Dockerfile .
+# Build the Synapse monolith image from Complement, based on the above image we just built
+docker build -t complement-synapse -f "$COMPLEMENT_DIR/dockerfiles/Synapse.Dockerfile" "$COMPLEMENT_DIR/dockerfiles"
 
-# Download Complement
-wget -N https://github.com/matrix-org/complement/archive/master.tar.gz
-tar -xzf master.tar.gz
-cd complement-master
+cd "$COMPLEMENT_DIR"
 
-# Build the Synapse image from Complement, based on the above image we just built
-docker build -t complement-synapse -f dockerfiles/Synapse.Dockerfile ./dockerfiles
+EXTRA_COMPLEMENT_ARGS=""
+if [[ -n "$1" ]]; then
+  # A test name regex has been set, supply it to Complement
+  EXTRA_COMPLEMENT_ARGS+="-run $1 "
+fi
 
-# Run the tests on the resulting image!
-COMPLEMENT_BASE_IMAGE=complement-synapse go test -v -count=1 ./tests
+# Run the tests!
+COMPLEMENT_BASE_IMAGE=complement-synapse go test -v -tags synapse_blacklist -count=1 $EXTRA_COMPLEMENT_ARGS ./tests