diff --git a/tests/docker/dockerfiles/debian-bootstrap.docker b/tests/docker/dockerfiles/debian-bootstrap.docker
index 14212b9cf4600c7bde01b52341556c9c7b2b1c65..e13c26a7eda2e021d25540700e5b39b167ac57f0 100644
--- a/tests/docker/dockerfiles/debian-bootstrap.docker
+++ b/tests/docker/dockerfiles/debian-bootstrap.docker
@@ -9,6 +9,7 @@ FROM scratch
 ADD . /
 
 # Patch all mounts as docker already has stuff set up
+# (this is not needed for later debootstraps but is harmless atm)
 RUN sed -i 's/in_target mount/echo not for docker in_target mount/g' /debootstrap/functions
 
 # Run stage 2