diff --git a/tools/run-centos b/tools/run-centos
index baa86b25..f5b961f9 100755
--- a/tools/run-centos
+++ b/tools/run-centos
@@ -153,7 +153,7 @@ start_container() {
     if [ ! -z "${http_proxy-}" ]; then
         debug 1 "configuring proxy ${http_proxy}"
         inside "$name" sh -c "echo proxy=$http_proxy >> /etc/yum.conf"
-        inside "$name" sh -c "sed -i s/enabled=1/enabled=0/ /etc/yum/pluginconf.d/fastestmirror.conf"
+        inside "$name" "sed -i s/enabled=1/enabled=0/ /etc/yum/pluginconf.d/fastestmirror.conf"
     fi
 }