diff --git a/nixos/modules/misc/ids.nix b/nixos/modules/misc/ids.nix
index e3edc9dda6b6..73134414138b 100644
--- a/nixos/modules/misc/ids.nix
+++ b/nixos/modules/misc/ids.nix
@@ -106,6 +106,7 @@
       firebird = 95;
       redis = 96;
       haproxy = 97;
+      mongodb = 98;
 
       # When adding a uid, make sure it doesn't match an existing gid.
 
diff --git a/nixos/modules/services/databases/mongodb.nix b/nixos/modules/services/databases/mongodb.nix
index d62994158939..213a60687b23 100644
--- a/nixos/modules/services/databases/mongodb.nix
+++ b/nixos/modules/services/databases/mongodb.nix
@@ -90,8 +90,9 @@ in
 
   config = mkIf config.services.mongodb.enable {
 
-    users.extraUsers = singleton
-      { name = cfg.user;
+    users.extraUsers.mongodb = mkIf (cfg.user == "mongodb")
+      { name = "mongodb";
+        uid = config.ids.uids.mongodb;
         description = "MongoDB server user";
       };