diff --git a/config.nix b/config.nix
index e971e3b5..9a250617 100644
--- a/config.nix
+++ b/config.nix
@@ -51,6 +51,8 @@ let
       environment.etc."tmux.conf".text = ''
         source-file ${config.system.build.setTmuxOptions}
 
+        bind 0 set status
+
         set -g status-bg black
         set -g status-fg white
       '';
@@ -65,9 +67,10 @@ let
         bindkey -e
         setopt autocd
 
-        export PROMPT='%B%(?..[%?] )%b> '
+        export PROMPT='%B%(?..[%?] )%b⇒ '
         export RPROMPT='%F{green}%~%f'
 
+        export PATH=/var/run/current-system/sw/bin:/var/run/current-system/sw/bin''${PATH:+:$PATH}
         export PATH=/nix/var/nix/profiles/default/bin:/nix/var/nix/profiles/default/sbin''${PATH:+:$PATH}
         export PATH=$HOME/.nix-profile/bin:$HOME/.nix-profile/bin''${PATH:+:$PATH}
 
@@ -76,10 +79,10 @@ let
 
         nixdarwin-rebuild () {
           case $1 in
-            "build")  nix-build --no-out-link "<nixpkgs>" -A nixdarwin.toplevel ;;
+            "build")  nix-build --no-out-link '<nixpkgs>' -A nixdarwin.toplevel ;;
             "repl")   nix-repl "$HOME/.nixpkgs/config.nix" ;;
-            "shell")  nix-shell "<nixpkgs>" -p nixdarwin.toplevel --run "zsh -l" ;;
-            "switch") nix-env -f "<nixpkgs>" -iA nixdarwin.toplevel && exec zsh -l ;;
+            "shell")  nix-shell '<nixpkgs>' -p nixdarwin.toplevel --run "zsh -l" ;;
+            "switch") nix-env -f '<nixpkgs>' -iA nixdarwin.toplevel && nix-shell '<nixpkgs>' -A nixdarwin.toplevel --run 'sudo $out/activate'  && exec zsh -l ;;
             "")       return 1 ;;
           esac
         }
diff --git a/modules/system.nix b/modules/system.nix
index a0d27620..49820593 100644
--- a/modules/system.nix
+++ b/modules/system.nix
@@ -26,6 +26,11 @@ in {
       '';
     };
 
+    system.nixdarwinLabel = mkOption {
+      type = types.str;
+      default = "16.09";
+    };
+
     # Used by <nixos/modules/system/etc/etc.nix>
     system.activationScripts = mkOption { internal = true; };
 
@@ -33,9 +38,43 @@ in {
 
   config = {
 
-    system.build.toplevel = pkgs.buildEnv {
-      name = "nixdarwin-system";
-      paths = [ cfg.path cfg.build.etc ];
+    system.activationScripts.script = ''
+      #! ${pkgs.stdenv.shell}
+
+      systemConfig=@out@
+
+      # Make this configuration the current configuration.
+      # The readlink is there to ensure that when $systemConfig = /system
+      # (which is a symlink to the store), /run/current-system is still
+      # used as a garbage collection root.
+      ln -sfn "$(readlink -f "$systemConfig")" /run/current-system
+
+      # Prevent the current configuration from being garbage-collected.
+      ln -sfn /run/current-system /nix/var/nix/gcroots/current-system
+
+    '';
+
+    system.build.toplevel = pkgs.stdenvNoCC.mkDerivation {
+      name = "nixdarwin-system-${cfg.nixdarwinLabel}";
+      preferLocalBuild = true;
+
+      activationScript = config.system.activationScripts.script;
+      inherit (cfg) nixdarwinLabel;
+
+      buildCommand = ''
+        mkdir $out
+
+        ln -s ${cfg.build.etc}/etc $out/etc
+        ln -s ${cfg.path} $out/sw
+
+        echo "$activationScript" > $out/activate
+        substituteInPlace $out/activate --subst-var out
+        chmod u+x $out/activate
+        unset activationScript
+
+        echo -n "$nixdarwinLabel" > $out/nixdarwin-version
+        echo -n "$system" > $out/system
+      '';
     };
 
   };