diff --git a/modules/nix/default.nix b/modules/nix/default.nix
index 857c4be..b70487d 100644
--- a/modules/nix/default.nix
+++ b/modules/nix/default.nix
@@ -759,7 +759,7 @@ in
 
         # Not in NixOS module
         { assertion = elem "nixbld" config.users.knownGroups -> elem "nixbld" createdGroups; message = "refusing to delete group nixbld in users.knownGroups, this would break nix"; }
-        { assertion = elem "_nixbld1" config.users.knownGroups -> elem "_nixbld1" createdUsers; message = "refusing to delete user _nixbld1 in users.knownUsers, this would break nix"; }
+        { assertion = elem "_nixbld1" config.users.knownUsers -> elem "_nixbld1" createdUsers; message = "refusing to delete user _nixbld1 in users.knownUsers, this would break nix"; }
         { assertion = config.users.groups ? "nixbld" -> config.users.groups.nixbld.members != []; message = "refusing to remove all members from nixbld group, this would break nix"; }
 
         {