diff --git a/shadowsocks/Dockerfile b/shadowsocks/Dockerfile
index e4c1d3c..050e876 100644
--- a/shadowsocks/Dockerfile
+++ b/shadowsocks/Dockerfile
@@ -5,11 +5,10 @@
 FROM alpine
 MAINTAINER kev <noreply@datageek.info>
 
-RUN apk update \
-    && apk add curl python \
+RUN apk add --update curl python \
     && curl -sSL https://bootstrap.pypa.io/get-pip.py | python \
     && pip install shadowsocks \
-    && apk del curl \
+    && apk del --purge curl \
     && rm -rf /var/cache/apk/*
 
 ENV SERVER_ADDR 0.0.0.0
diff --git a/shadowsocks/libev/Dockerfile b/shadowsocks/libev/Dockerfile
index ca33966..468b530 100644
--- a/shadowsocks/libev/Dockerfile
+++ b/shadowsocks/libev/Dockerfile
@@ -10,15 +10,14 @@ ENV SS_URL https://github.com/shadowsocks/shadowsocks-libev/archive/v$SS_VER.tar
 ENV SS_DIR shadowsocks-libev-$SS_VER
 ENV SS_DEP curl linux-headers build-base autoconf libtool openssl-dev
 
-RUN apk update \
-    && apk add $SS_DEP \
+RUN apk add --update $SS_DEP \
     && curl -sSL $SS_URL | tar xz \
     && cd $SS_DIR \
         && ./configure \
         && make install \
         && cd .. \
         && rm -rf $SS_DIR \
-    && apk del $SS_DEP \
+    && apk del --purge $SS_DEP \
     && rm -rf /var/cache/apk/*
 
 ENV SERVER_ADDR 0.0.0.0