diff --git a/Dockerfile b/Dockerfile
index d8de0b2..d891bce 100644
--- a/Dockerfile
+++ b/Dockerfile
@@ -1,6 +1,7 @@
 FROM ubuntu
 
-RUN apt-get install -y wget firefox xfce4 vnc4server
+RUN apt-get update -y \
+    && apt-get install -y wget firefox xfce4 vnc4server
 ENV DISPLAY=":1" VNC_COL_DEPTH=24 VNC_RESOLUTION=1280x800 VNC_PW=xiaosong
 RUN mkdir /root/.vnc/ \
     && wget http://fpdownload.macromedia.com/get/flashplayer/pdc/11.2.202.635/install_flash_player_11_linux.x86_64.tar.gz \