diff --git a/flake.nix b/flake.nix
index 2378dfb..fefc2b6 100644
--- a/flake.nix
+++ b/flake.nix
@@ -79,6 +79,9 @@
           {
             home-manager.useGlobalPkgs = true;
             home-manager.useUserPackages = true;
+            # Back up pre-existing dotfiles (e.g. .zshrc) instead of aborting
+            # activation when home-manager would overwrite them.
+            home-manager.backupFileExtension = "backup";
           }
         ];
 
@@ -117,6 +120,9 @@
           {
             home-manager.useGlobalPkgs = true;
             home-manager.useUserPackages = true;
+            # Back up pre-existing dotfiles (e.g. .zshrc) instead of aborting
+            # activation when home-manager would overwrite them.
+            home-manager.backupFileExtension = "backup";
           }
         ];