diff --git a/modules/home-manager/nix/default.nix b/modules/home-manager/nix/default.nix
index c36b7f7..ce63241 100644
--- a/modules/home-manager/nix/default.nix
+++ b/modules/home-manager/nix/default.nix
@@ -25,4 +25,7 @@
     };
   };
   xdg.configFile."nixpkgs/config.nix".text = ''{ allowUnfree = true; }'';
+
+  # set home-manager to replace existing files on activation
+  backupFileExtension = "backup";
 }