diff --git a/image/prepare.sh b/image/prepare.sh
index 80d73c2..90d6a50 100755
--- a/image/prepare.sh
+++ b/image/prepare.sh
@@ -10,7 +10,8 @@ export INITRD=no
 mkdir -p /etc/container_environment
 echo -n no > /etc/container_environment/INITRD
 
-## Enable Ubuntu Universe and Multiverse.
+## Enable Ubuntu Universe, Multiverse, and deb-src for main.
+sed -i 's/^#\s*\(deb.*main restricted\)$/\1/g' /etc/apt/sources.list
 sed -i 's/^#\s*\(deb.*universe\)$/\1/g' /etc/apt/sources.list
 sed -i 's/^#\s*\(deb.*multiverse\)$/\1/g' /etc/apt/sources.list
 apt-get update