diff --git a/config-simple.hs b/config-simple.hs
index 3fb5918..94562ee 100644
--- a/config-simple.hs
+++ b/config-simple.hs
@@ -24,7 +24,8 @@ main = defaultMain hosts
 hosts :: [Host]
 hosts =
 	[ host "mybox.example.com"
-		& Apt.stdSourcesList Unstable
+		& os (System (Debian Unstable) "amd64")
+		& Apt.stdSourcesList
 		& Apt.unattendedUpgrades
 		& Apt.installed ["etckeeper"]
 		& Apt.installed ["ssh"]
@@ -36,7 +37,9 @@ hosts =
 		& Cron.runPropellor "30 * * * *"
 
 	-- A generic webserver in a Docker container.
-	, Docker.container "webserver" "joeyh/debian-unstable"
+	, Docker.container "webserver" "joeyh/debian-stable"
+		& os (System (Debian Stable) "amd64")
+		& Apt.stdSourcesList
 		& Docker.publish "80:80"
 		& Docker.volume "/var/www:/var/www"
 		& Apt.serviceInstalledRunning "apache2"
diff --git a/doc/haskell_newbie.mdwn b/doc/haskell_newbie.mdwn
index 8e14b35..f1a81e4 100644
--- a/doc/haskell_newbie.mdwn
+++ b/doc/haskell_newbie.mdwn
@@ -41,22 +41,24 @@ stub to go run itself. No need to ever change this part.
 hosts :: [Host]
 hosts =
     [ host "mybox.example.com"
-        & Apt.stdSourcesList Unstable
+    	& os (System (Debian Unstable) "amd64")
+        & Apt.stdSourcesList
     , host "server.example.com"
-        & Apt.stdSourcesList Stable
+    	& os (System (Debian Stable) "amd64")
+        & Apt.stdSourcesList
         & Apt.installed ["ssh"]
     ]
 """]]
 
 This defines a list of hosts, with two hosts in it. 
 
-The configuration for the mybox host tells propellor to configure its
-`/etc/apt/sources.list` to use Debian `Unstable`.
-Of course you might want to change that to `Stable`.
+The configuration for the mybox host first tells propellor what
+OS it's running. Then the `stdSourcesList` line tells propellor to
+configure its `/etc/apt/sources.list`, using its OS.
+(Of course you might want to change that `Unstable` to `Stable`.)
 
 Each property of the host is prefixed with an "&" operator. This just makes
-a list of properties. Above, the first host has only 1 property, while
-the second host has 2 properties.
+a list of properties.
 
 Some other properties you may find in your config.hs, or want to add: