diff --git a/system/switch-to-configuration.sh b/system/switch-to-configuration.sh
index dcca984282b1..eaeb3106afd9 100644
--- a/system/switch-to-configuration.sh
+++ b/system/switch-to-configuration.sh
@@ -35,6 +35,18 @@ fi
 
 if test "$action" = "switch" -o "$action" = "test"; then
 
+    oldVersion=$(cat /var/run/current-system/upstart-interface-version 2> /dev/null || echo 0)
+    newVersion=$(cat @out@/upstart-interface-version 2> /dev/null || echo 0)
+
+    if test "$oldVersion" -ne "$newVersion"; then
+        cat <<EOF
+Warning: the new NixOS configuration has an Upstart version that is
+incompatible with the current version.  The new configuration won't
+take effect until you reboot the system.
+EOF
+        exit 1
+    fi
+
     oldEvents=$(readlink -f /etc/event.d || true)
     newEvents=$(readlink -f @out@/etc/event.d)
 
diff --git a/system/system.nix b/system/system.nix
index ef4e027848b5..d4507258a341 100644
--- a/system/system.nix
+++ b/system/system.nix
@@ -227,6 +227,7 @@ rec {
       pkgs.diffutils
       pkgs.upstart # for initctl
     ];
+    upstartInterfaceVersion = pkgs.upstart.interfaceVersion;
     # This attribute is responsible for creating boot entries for 
     # child configuration. They are only (directly) accessible
     # when the parent configuration is boot default. For example,
diff --git a/system/system.sh b/system/system.sh
index 95f650f39aaa..67042b5faf45 100644
--- a/system/system.sh
+++ b/system/system.sh
@@ -13,6 +13,7 @@ ln -s $upstart $out/upstart
 
 echo "$kernelParams" > $out/kernel-params
 echo "$configurationName" > $out/configuration-name
+echo "$upstartInterfaceVersion" > $out/upstart-interface-version
 
 mkdir $out/fine-tune
 ChildCount=0;
diff --git a/upstart-jobs/sshd.nix b/upstart-jobs/sshd.nix
index 03dc9f47a9c3..d6c06b24f7e3 100644
--- a/upstart-jobs/sshd.nix
+++ b/upstart-jobs/sshd.nix
@@ -45,7 +45,7 @@ let
         gatewayPorts = mkOption {
           default = "no";
           description = "
-             Specifies  whether  remote hosts are allowed to connect to ports forwarded for the client. See man sshd_conf.
+             Specifies whether remote hosts are allowed to connect to ports forwarded for the client. See man sshd_conf.
             ";
           };
       };