diff --git a/Dockerfile b/Dockerfile
index c62cc3b..ed7d882 100644
--- a/Dockerfile
+++ b/Dockerfile
@@ -4,6 +4,7 @@ MAINTAINER Netz39 Administrators <admin@netz39.de>
 RUN apt-get update \
     && DEBIAN_FRONTEND=noninteractive apt-get install -y --no-install-recommends --no-install-suggests \
         mercurial \
-        telnet
+        telnet \
+    && rm -rf /var/lib/apt/lists/*
 
 RUN hg clone https://hg.prosody.im/prosody-modules/ /usr/local/lib/prosody-modules