diff --git a/.docker/Makefile b/.docker/Makefile
index 28024901..ea8306ff 100644
--- a/.docker/Makefile
+++ b/.docker/Makefile
@@ -1,10 +1,14 @@
 IMAGE="dwarfs-buildenv"
 
 ROOT_DIR:=$(shell dirname $(realpath $(firstword $(MAKEFILE_LIST))))
+NPROC:=$(shell nproc)
 
 build:
 	docker build -t $(IMAGE) .
 
+build_arm:
+	docker build -t $(IMAGE) --build-arg ARCH=arm64v8 .
+
 run:
 	@docker run -it --rm \
             --cap-add SYS_ADMIN --device /dev/fuse --privileged \
@@ -12,5 +16,5 @@ run:
             --mount type=bind,source="$(ROOT_DIR)"/../@docker-ccache,target=/ccache \
             --mount type=bind,source="$(ROOT_DIR)"/../@docker-home,target=/home/ubuntu \
             --mount type=bind,source="$(ROOT_DIR)"/../@docker-build,target=/home/ubuntu/build \
-            --env CCACHE_DIR=/ccache --env CTEST_PARALLEL_LEVEL=$(nproc) \
+            --env CCACHE_DIR=/ccache --env CTEST_PARALLEL_LEVEL=$(NPROC) \
             --entrypoint /bin/bash $(IMAGE)