diff --git a/linux-build-farm/centos-6/x64/Dockerfile b/linux-build-farm/centos-6/x64/Dockerfile
index 10a2bf169..8ae110aa9 100644
--- a/linux-build-farm/centos-6/x64/Dockerfile
+++ b/linux-build-farm/centos-6/x64/Dockerfile
@@ -3,9 +3,12 @@ MAINTAINER Adam Ierymenko <adam.ierymenko@zerotier.com>
 
 RUN yum update -y
 RUN yum install -y epel-release
-RUN yum install -y clang make development-tools rpmdevtools http-parser-devel lz4-devel libnatpmp-devel
+RUN yum install -y make development-tools rpmdevtools http-parser-devel lz4-devel libnatpmp-devel
+
+RUN yum install -y centos-release-scl
+RUN yum install -y devtoolset-4-gcc-c++
+
+RUN ln -sf /opt/rh/devtoolset-4/root/usr/bin/gcc /usr/bin/gcc
+RUN ln -sf /opt/rh/devtoolset-4/root/usr/bin/g++ /usr/bin/g++
 
 ADD zt1-src.tar.gz /
-
-#RUN ln -sf /usr/bin/clang++-3.5 /usr/bin/clang++
-#RUN ln -sf /usr/bin/clang-3.5 /usr/bin/clang
diff --git a/linux-build-farm/centos-6/x86/Dockerfile b/linux-build-farm/centos-6/x86/Dockerfile
index d9ea0f6e4..1e0da5704 100644
--- a/linux-build-farm/centos-6/x86/Dockerfile
+++ b/linux-build-farm/centos-6/x86/Dockerfile
@@ -3,9 +3,21 @@ MAINTAINER Adam Ierymenko <adam.ierymenko@zerotier.com>
 
 RUN yum update -y
 RUN yum install -y epel-release
-RUN yum install -y clang make development-tools rpmdevtools http-parser-devel lz4-devel libnatpmp-devel
+RUN yum install -y make development-tools rpmdevtools http-parser-devel lz4-devel libnatpmp-devel
+
+#RUN rpm --import http://ftp.scientificlinux.org/linux/scientific/5x/x86_64/RPM-GPG-KEYs/RPM-GPG-KEY-cern
+#RUN curl http://linuxsoft.cern.ch/cern/devtoolset/slc6-devtoolset.repo >/etc/yum.repos.d/slc6-devtoolset.repo
+#RUN yum install -y devtoolset-2-gcc-c++
+
+#RUN ln -sf /opt/rh/devtoolset-2/root/usr/bin/gcc /usr/bin/gcc
+#RUN ln -sf /opt/rh/devtoolset-2/root/usr/bin/g++ /usr/bin/g++
+
+RUN yum install -y clang
+RUN yum install -y gcc-c++
 
 ADD zt1-src.tar.gz /
 
-#RUN ln -sf /usr/bin/clang++-3.5 /usr/bin/clang++
-#RUN ln -sf /usr/bin/clang-3.5 /usr/bin/clang
+RUN mv /ZeroTierOne/make-linux.mk /ZeroTierOne/make-linux.mk.old
+RUN echo 'CFLAGS=-O3 -fstack-protector' >/ZeroTierOne/make-linux.mk
+RUN echo 'CXXFLAGS=-O3 -fstack-protector' >>/ZeroTierOne/make-linux.mk
+RUN cat /ZeroTierOne/make-linux.mk.old >>/ZeroTierOne/make-linux.mk