diff --git a/ci/README.md b/ci/README.md
index af29f7c..1614c79 100644
--- a/ci/README.md
+++ b/ci/README.md
@@ -2,13 +2,20 @@
 
 ## Re-building an image after updating the docker file
 
-Run `docker build -t snmallocciteam/$IMG:latest -f ci/$IMG .` from the root of the repo,
-where `$IMG` is the image you want to rebuild, for example `build_linux_x64`
+Run `docker build -t snmallocciteam/build_${IMG}:latest -f ci/${IMG} .` from the root of the repo,
+where `$IMG` is the image you want to rebuild, for example `linux_x64`
 
 If you are building a multiarch image, ie. an image targeting an architecture other than
 the one you are running, you will need to install the qemu handler before you can build:
 `sudo docker run --rm --privileged multiarch/qemu-user-static:register --reset`
 
+## Testing locally
+
+Having built a docker image, you can build your current tree therein with
+
+    docker run --rm -u $(id -u) -v ${PWD}:/opt:ro snmallocciteam/build_${IMG}:latest \
+      sh -c "cd /tmp; CC=clang-10 CXX=clang++-10 BUILD_TYPE=Debug SNMALLOC_SRC=/opt /opt/ci/scripts/build.sh && (cd build; ninja test)"
+
 ## Pushing the updated docker image to Docker Hub
 
 Run `docker push snmallocciteam/$IMG:latest`