diff --git a/polipo/Dockerfile b/polipo/Dockerfile
index f21e400..94bf03b 100644
--- a/polipo/Dockerfile
+++ b/polipo/Dockerfile
@@ -5,7 +5,8 @@
 FROM alpine
 MAINTAINER kev <noreply@easypi.info>
 
-RUN apk add -U build-base openssl \
+RUN set -xe \
+    && apk add --no-cache build-base openssl \
     && wget https://github.com/jech/polipo/archive/master.zip -O polipo.zip \
     && unzip polipo.zip \
     && cd polipo-master \
@@ -14,8 +15,7 @@ RUN apk add -U build-base openssl \
     && cd .. \
     && rm -rf polipo.zip polipo-master \
     && mkdir -p /usr/share/polipo/www /var/cache/polipo \
-    && apk del build-base openssl \
-    && rm -rf /var/cache/apk/*
+    && apk del build-base openssl
 
 EXPOSE 8123
 
diff --git a/polipo/README.md b/polipo/README.md
index 2f8350b..a793bac 100644
--- a/polipo/README.md
+++ b/polipo/README.md
@@ -1,17 +1,19 @@
 Polipo — a caching web proxy
 ============================
 
-`Polipo` is a small and fast caching web proxy (a web cache, an HTTP proxy, a
+[Polipo][1] is a small and fast caching web proxy (a web cache, an HTTP proxy, a
 proxy server). While Polipo was designed to be used by one person or a small
 group of people, there is nothing that prevents it from being used by a larger
 group.
 
 ## docker-compose.yml
 
-```
+```yaml
 polipo:
   image: vimagick/polipo
-  command: authCredentials=username:password
+  command:
+    authCredentials=username:password
+    socksParentProxy=1.2.3.4:9050
   ports:
     - "8123:8123"
   restart: always
@@ -19,12 +21,14 @@ polipo:
 
 ## server
 
-```
+```bash
 $ docker-compose up -d
 ```
 
 ## client
 
-```
+```bash
 $ curl -x http://username:password@server:8123 https://www.youtube.com/
 ```
+
+[1]: https://www.irif.univ-paris-diderot.fr/~jch/software/polipo/
diff --git a/polipo/docker-compose.yml b/polipo/docker-compose.yml
index 2981ab8..8953652 100644
--- a/polipo/docker-compose.yml
+++ b/polipo/docker-compose.yml
@@ -1,6 +1,8 @@
 polipo:
   image: vimagick/polipo
-  command: authCredentials=username:password
+  command:
+    authCredentials=username:password
+    socksParentProxy=1.2.3.4:9050
   ports:
     - "8123:8123"
   restart: always