diff --git a/manjarolinux/Dockerfile b/manjarolinux/Dockerfile
index 71e51e7..4c614d5 100644
--- a/manjarolinux/Dockerfile
+++ b/manjarolinux/Dockerfile
@@ -15,6 +15,7 @@ RUN mkdir /home/takano32
 RUN chown -R takano32.takano32 /build-kernel /home/takano32
 RUN echo "takano32 ALL=(ALL:ALL) NOPASSWD: ALL" > /etc/sudoers.d/takano32
 ENV SUDO="sudo -u takano32"
+RUN echo 'export MAKEFLAGS="-j 8"' >> /etc/bash.bashrc
 
 COPY ./manjarolinux/entrypoint.sh /
 RUN chmod 755 /entrypoint.sh
diff --git a/manjarolinux/entrypoint.sh b/manjarolinux/entrypoint.sh
index 59eacba..f5f2a80 100644
--- a/manjarolinux/entrypoint.sh
+++ b/manjarolinux/entrypoint.sh
@@ -4,6 +4,7 @@ set -eux
 BUILD_DIR=/build-kernel/build
 SUDO="sudo -u takano32"
 
+rm -rf $BUILD_DIR/* || :
 mkdir -p $BUILD_DIR
 chown -R takano32:takano32 $BUILD_DIR
 cd $BUILD_DIR
@@ -17,10 +18,7 @@ $SUDO git config --global http.postBuffer 524288000
 while :; do $SUDO makepkg -o --skippgpcheck && break || sleep 5; done
 
 # `makepkg` in `$BUILD_DIR/linux`
-JOBS=$(getconf _NPROCESSORS_ONLN)
-JOBS=$(expr "$JOBS" + "$JOBS")
-MAKEFLAGS="-j $JOBS"
-$SUDO bash -c "MAKEFLAGS=""$MAKEFLAGS"" makepkg --skippgpcheck"
+$SUDO makepkg --skippgpcheck
 
 cd $BUILD_DIR
 mv linux/src/archlinux-linux/Documentation/output ../htmldocs