Document that the `DOCKER_BUILDKIT=1` flag is needed to build the docker image. (#13515)

1 files changed, 1 insertions, 1 deletions

diff --git a/docker/README.md b/docker/README.md

index 5b7de2fe38..017f046c58 100644
--- a/docker/README.md
+++ b/docker/README.md
@@ -191,7 +191,7 @@ If you need to build the image from a Synapse checkout, use the following `docke
  build` command from the repo's root:
 
 ```
-docker build -t matrixdotorg/synapse -f docker/Dockerfile .
+DOCKER_BUILDKIT=1 docker build -t matrixdotorg/synapse -f docker/Dockerfile .
 ```
 
 You can choose to build a different docker image by changing the value of the `-f` flag to