@@ -11,6 +11,7 @@ DOCKERFILE := $(shell bash -c 'source hack/make/.detect-daemon-osarch && echo $$

 # to allow things like `make KEEPBUNDLE=1 binary` easily

 # `project/PACKAGERS.md` have some limited documentation of some of these

 DOCKER_ENVS := \

+	-e BUILD_APT_MIRROR \

 	-e BUILDFLAGS \

 	-e KEEPBUNDLE \

 	-e DOCKER_BUILD_ARGS \

@@ -60,6 +61,7 @@ DOCKER_PORT_FORWARD := $(if $(DOCKER_PORT),-p "$(DOCKER_PORT)",)

 DOCKER_FLAGS := docker run --rm -i --privileged $(DOCKER_ENVS) $(DOCKER_MOUNT) $(DOCKER_PORT_FORWARD)

 BUILD_APT_MIRROR := $(if $(DOCKER_BUILD_APT_MIRROR),--build-arg APT_MIRROR=$(DOCKER_BUILD_APT_MIRROR))

+export BUILD_APT_MIRROR

 # if this session isn't interactive, then we don't want to allocate a

 # TTY, which would fail, but if it is interactive, we do want to attach

@@ -52,7 +52,14 @@ set -e

 		image="dockercore/builder-deb:$version"

 		if ! docker inspect "$image" &> /dev/null; then

-			( set -x && docker build ${DOCKER_BUILD_ARGS} -t "$image" "$dir" )

+			(

+				# Add the APT_MIRROR args only if the consuming Dockerfile uses it

+				# Otherwise this will cause the build to fail

+				if [ "$(grep 'ARG APT_MIRROR=' $dir/Dockerfile)" ] && [ "$BUILD_APT_MIRROR" ]; then

+					DOCKER_BUILD_ARGS="$DOCKER_BUILD_ARGS $BUILD_APT_MIRROR"

+				fi

+				set -x && docker build ${DOCKER_BUILD_ARGS} -t "$image" "$dir"

+			)

 		fi

 		mkdir -p "$DEST/$version"