diff --git a/tests/docker/dockerfiles/travis.docker b/tests/docker/dockerfiles/travis.docker
index 03ebfb0ef2..46cf367488 100644
--- a/tests/docker/dockerfiles/travis.docker
+++ b/tests/docker/dockerfiles/travis.docker
@@ -2,7 +2,7 @@ FROM travisci/ci-garnet:packer-1512502276-986baf0
 ENV DEBIAN_FRONTEND noninteractive
 ENV LANG en_US.UTF-8
 ENV LC_ALL en_US.UTF-8
-RUN cat /etc/apt/sources.list | sed "s/# deb-src/deb-src/" >> /etc/apt/sources.list
+RUN sed -i "s/# deb-src/deb-src/" /etc/apt/sources.list
 RUN apt-get update
 RUN apt-get -y build-dep qemu
 RUN apt-get -y install device-tree-compiler python2.7 python-yaml dh-autoreconf gdb strace lsof net-tools gcovr