diff --git a/pptpd/Dockerfile b/pptpd/Dockerfile
index 8b484a4..6b6fea1 100644
--- a/pptpd/Dockerfile
+++ b/pptpd/Dockerfile
@@ -5,8 +5,10 @@
 FROM alpine
 MAINTAINER kev<noreply@datageek.info>
 
-RUN apk update \
-    && apk add iptables ppp pptpd \
+RUN set -xe \
+    && apk add -U iptables \
+                  ppp \
+                  pptpd \
     && rm -rf /var/cache/apk/*
 
 COPY pptpd.conf    /etc/
@@ -15,6 +17,7 @@ COPY pptpd-options /etc/ppp/
 
 EXPOSE 1723
 
-CMD iptables -t nat -A POSTROUTING -o eth0 -j MASQUERADE \
+CMD set -xe \
+    && iptables -t nat -A POSTROUTING -o eth0 -j MASQUERADE \
     && pptpd \
     && syslogd -n -O /dev/stdout