diff --git a/nixos/modules/config/users-groups.nix b/nixos/modules/config/users-groups.nix
index 11e969b760e..31435039e56 100644
--- a/nixos/modules/config/users-groups.nix
+++ b/nixos/modules/config/users-groups.nix
@@ -35,6 +35,7 @@ let
 
       name = mkOption {
         type = types.str;
+        apply = x: assert (builtins.stringLength x < 32 || abort "Username '${x}' is longer than 31 characters which is not allowed!"); x;
         description = ''
           The name of the user account. If undefined, the name of the
           attribute set will be used.
@@ -91,6 +92,7 @@ let
 
       group = mkOption {
         type = types.str;
+        apply = x: assert (builtins.stringLength x < 17 || abort "Group name '${x}' is longer than 16 characters which is not allowed!"); x;
         default = "nogroup";
         description = "The user's primary group.";
       };