diff --git a/infra/setup/bin/backup_file b/infra/setup/bin/backup_file
index 3b62026e7..051dd4d6c 100755
--- a/infra/setup/bin/backup_file
+++ b/infra/setup/bin/backup_file
@@ -13,9 +13,10 @@ source "$DOTFILES/infra/scripts/prompts.sh"
 #   - {string} [extension = bak] - extension of created file, default of bak
 backup_file() {
   # parameters
-  local src="$1" ext="$2"
+  local src="$1" ext="${2:-bak}"
 
   [ -f "$src" ] && {
+    # TODO: conditionally use sudo here
     sudo mv "$src" "$src.$ext"
   }
 }
diff --git a/infra/setup/bin/setup_nix b/infra/setup/bin/setup_nix
index d3b2badbe..8bf67d698 100755
--- a/infra/setup/bin/setup_nix
+++ b/infra/setup/bin/setup_nix
@@ -172,13 +172,13 @@ maybe_install_nix_darwin() {
 
   nix-build https://github.com/LnL7/nix-darwin/archive/master.tar.gz -A installer
 
-  backup_default_system_files
+  # backup_default_system_files
 
   # TODO: handle interactive prompts, pass flags to answer questions?
   source "${TMPDIR}/result/bin/darwin-installer" || {
     fail '`nix-darwin` installer failed. Please fix any issues and try again.'
 
-    restore_default_system_files
+    # restore_default_system_files
 
     return 1
   }