diff --git a/changelog.d/12541.docker b/changelog.d/12541.docker
new file mode 100644
index 0000000000..c3b9c31657
--- /dev/null
+++ b/changelog.d/12541.docker
@@ -0,0 +1 @@
+Explicitly opt-in to using [BuildKit-specific features](https://github.com/moby/buildkit/blob/master/frontend/dockerfile/docs/syntax.md) in the Dockerfile. This fixes issues with building images in some GitLab CI environments.
diff --git a/docker/Dockerfile b/docker/Dockerfile
index 4523c60645..ccc6a9f778 100644
--- a/docker/Dockerfile
+++ b/docker/Dockerfile
@@ -1,3 +1,4 @@
+# syntax=docker/dockerfile:1
 # Dockerfile to build the matrixdotorg/synapse docker images.
 #
 # Note that it uses features which are only available in BuildKit - see