diff --git a/nixos.nix b/nixos.nix
index 307355b..cde560c 100644
--- a/nixos.nix
+++ b/nixos.nix
@@ -9,6 +9,7 @@ packages:
 let
   inherit (lib)
     lists
+    attrsets
     mkMerge
     mkIf
     mapAttrs
@@ -231,25 +232,48 @@ in
       {
         useUserPackages = false; # prevent users.users entries from being added
 
-        users = mkMerge (
-          foldlAttrs (
-            acc: _: fid:
-            acc
-            ++ foldlAttrs (
-              acc': _: app:
-              acc'
-              ++ [
-                {
-                  ${getsubname fid app.identity} = mkMerge [
-                    cfg.extraHomeConfig
-                    app.extraConfig
-                    { home.packages = app.packages; }
-                  ];
-                }
-              ]
-            ) [ { ${getsubname fid 0} = cfg.extraHomeConfig; } ] cfg.apps
-          ) [ privPackages ] cfg.users
-        );
+        users =
+          mkMerge
+            (foldlAttrs
+              (
+                acc: _: fid:
+                foldlAttrs
+                  (
+                    acc: _: app:
+                    (
+                      let
+                        key = getsubname fid app.identity;
+                      in
+                      {
+                        usernames = acc.usernames // {
+                          ${key} = true;
+                        };
+                        merge = acc.merge ++ [
+                          {
+                            ${key} = mkMerge (
+                              [
+                                cfg.extraHomeConfig
+                                { home.packages = app.packages; }
+                              ]
+                              ++ lib.optional (!attrsets.hasAttrByPath [ key ] acc.usernames) app.extraConfig
+                            );
+                          }
+                        ];
+                      }
+                    )
+                  )
+                  {
+                    inherit (acc) usernames;
+                    merge = acc.merge ++ [ { ${getsubname fid 0} = cfg.extraHomeConfig; } ];
+                  }
+                  cfg.apps
+              )
+              {
+                usernames = { };
+                merge = [ privPackages ];
+              }
+              cfg.users
+            ).merge;
       };
 
     users =
diff --git a/test/configuration.nix b/test/configuration.nix
index 0bee0b2..4bd1ea5 100644
--- a/test/configuration.nix
+++ b/test/configuration.nix
@@ -95,14 +95,23 @@
     stateDir = "/var/lib/fortify";
     users.alice = 0;
 
-    extraHomeConfig = {
-      home.stateVersion = "23.05";
-    };
+    extraHomeConfig =
+      { config, ... }:
+      {
+        # To test merge deduplication:
+        options._fortify.stateVersion = lib.mkOption { type = lib.types.str; };
+
+        config = {
+          home = { inherit (config._fortify) stateVersion; };
+          _fortify.stateVersion = "23.05";
+        };
+      };
 
     apps = {
       "cat.gensokyo.extern.foot.noEnablements" = {
         name = "ne-foot";
         identity = 1;
+        shareUid = true;
         verbose = true;
         share = pkgs.foot;
         packages = with pkgs; [
@@ -130,7 +139,8 @@
 
       "cat.gensokyo.extern.Alacritty.x11" = {
         name = "x11-alacritty";
-        identity = 3;
+        identity = 1;
+        shareUid = true;
         verbose = true;
         share = pkgs.alacritty;
         packages = with pkgs; [
diff --git a/test/test.py b/test/test.py
index b912d6e..4b67b6f 100644
--- a/test/test.py
+++ b/test/test.py
@@ -206,9 +206,9 @@ machine.wait_until_fails("pgrep foot", timeout=5)
 
 # Test XWayland (foot does not support X):
 swaymsg("exec x11-alacritty")
-wait_for_window(f"u0_a{aid(2)}@machine")
+wait_for_window(f"u0_a{aid(0)}@machine")
 machine.send_chars("clear; glinfo && touch /tmp/x11-ok\n")
-machine.wait_for_file(tmpdir_path(2, "x11-ok"), timeout=15)
+machine.wait_for_file(tmpdir_path(0, "x11-ok"), timeout=15)
 collect_state_ui("alacritty_x11")
 check_state("x11-alacritty", 2)
 machine.send_chars("exit\n")