diff --git a/nixos/modules/system/boot/systemd/userdbd.nix b/nixos/modules/system/boot/systemd/userdbd.nix
index 8d70afea7f55..8f88f0960433 100644
--- a/nixos/modules/system/boot/systemd/userdbd.nix
+++ b/nixos/modules/system/boot/systemd/userdbd.nix
@@ -2,6 +2,12 @@
 
 let
   cfg = config.services.userdbd;
+
+  # List of system users that will be incorrectly treated as regular/normal
+  # users by userdb.
+  highSystemUsers = lib.filter (
+    user: user.enable && user.isSystemUser && (lib.defaultTo 0 user.uid) >= 1000 && user.uid != 65534
+  ) (lib.attrValues config.users.users);
 in
 {
   options.services.userdbd = {
@@ -14,6 +20,14 @@ in
       enables modifying public keys at runtime, either by users managed by
       {option}`services.homed`, or globally via drop-in files
     '';
+
+    silenceHighSystemUsers = lib.mkOption {
+      type = lib.types.bool;
+      default = false;
+      example = true;
+      description = "Silence warning about system users with high UIDs.";
+      visible = false;
+    };
   };
 
   config = lib.mkIf cfg.enable {
@@ -22,6 +36,28 @@ in
       message = "OpenSSH userdb integration requires security wrappers.";
     };
 
+    warnings = lib.optional (lib.length highSystemUsers > 0 && !cfg.silenceHighSystemUsers) ''
+      The following system users have UIDs higher than 1000:
+
+      ${lib.concatLines (lib.map (user: user.name) highSystemUsers)}
+
+      These users will be recognized by systemd-userdb as "regular" users, not
+      "system" users. This will affect programs that query regular users, such
+      as systemd-homed, which will not run the first boot user creation flow,
+      as regular users already exist.
+
+      To fix this issue, please remove or redefine these system users to have
+      UIDs below 1000. For Nix build users, it's possible to adjust the base
+      build user ID using the `ids.uids.nixbld` option, however care must be
+      taken to avoid collisions with UIDs of other services. Alternatively, you
+      may enable the `auto-allocate-uids` experimental feature and option in
+      the Nix configuration to avoid creating these users, however please note
+      that this option is experimental and subject to change.
+
+      Alternatively, to acknowledge and silence this warning, set
+      `services.userdbd.silenceHighSystemUsers` to true.
+    '';
+
     systemd.additionalUpstreamSystemUnits = [
       "systemd-userdbd.socket"
       "systemd-userdbd.service"