diff --git a/Dockerfile b/Dockerfile
index 88a1ee2..163dcf2 100644
--- a/Dockerfile
+++ b/Dockerfile
@@ -4,7 +4,7 @@
 FROM alpine
 
 # Change to http respositories, so they we can cache the install packages
-RUN if [ -n ${HTTP_PROXY} ] ; then sed -ie s'/https/http/' /etc/apk/repositories; fi
+RUN if [ -n ${HTTP_PROXY} ] ; then sed -i -e s'/https/http/' /etc/apk/repositories; fi
 
 RUN apk add shadow && groupadd -g 48 apache && useradd -d /opt/otrs -g apache -c 'OTRS user' otrs