diff --git a/builder/Dockerfile b/builder/Dockerfile
index 15650873..2e563572 100644
--- a/builder/Dockerfile
+++ b/builder/Dockerfile
@@ -1,10 +1,15 @@
 ARG base_image
 FROM ${base_image}
 
-RUN yum -y install gcc gcc-c++ make patch git curl && \
+COPY setup_yum_centos7.sh /
+
+# Run twice for EPEL.
+RUN /setup_yum_centos7.sh && \
+    yum -y install gcc gcc-c++ make patch git curl && \
     yum -y install bzip2-devel openssl-devel readline-devel libffi-devel && \
     yum -y install epel-release && \
     yum-config-manager --disable epel && \
+    /setup_yum_centos7.sh && \
     yum -y install --enablerepo=epel openssl11-devel && \
     yum clean all
 
@@ -19,8 +24,10 @@ COPY setup_python.sh /
 RUN /setup_python.sh "${python_versions}" "${cython_version}" "${fastrlock_version}"
 
 # Install devtoolset (g++) for CuPy v8 build.
-COPY setup_devtoolset.sh /
-RUN /setup_devtoolset.sh
+RUN yum install -y centos-release-scl && \
+    /setup_yum_centos7.sh && \
+    yum install -y devtoolset-7-gcc-c++ && \
+    yum clean all
 
 # Install additional libraries for CUDA.
 COPY cuda_lib/ /cuda_lib
diff --git a/builder/setup_devtoolset.sh b/builder/setup_devtoolset.sh
deleted file mode 100755
index ae827867..00000000
--- a/builder/setup_devtoolset.sh
+++ /dev/null
@@ -1,8 +0,0 @@
-#!/bin/bash -uex
-
-yum install -y centos-release-scl
-
-# CentOS 7
-yum install -y devtoolset-7-gcc-c++
-
-yum clean all
diff --git a/builder/setup_yum_centos7.sh b/builder/setup_yum_centos7.sh
new file mode 100755
index 00000000..959d11e9
--- /dev/null
+++ b/builder/setup_yum_centos7.sh
@@ -0,0 +1,5 @@
+#!/bin/bash -uex
+
+sed -i -E -e 's|^mirrorlist=|#mirrorlist=|g' /etc/yum.repos.d/*.repo
+sed -i -E -e 's|^#( ?)baseurl=http://mirror.centos.org/centos/(7\|\$releasever)/|baseurl=http://ftp.jaist.ac.jp/pub/Linux/CentOS-vault/7.9.2009/|g' /etc/yum.repos.d/*.repo
+sed -i -E -e 's|^#( ?)baseurl=http://download.fedoraproject.org/pub/epel/7/|baseurl=http://ftp.jaist.ac.jp/pub/Linux/Fedora/epel/7/|g' /etc/yum.repos.d/*.repo