diff --git a/.config/home-manager/home.nix b/.config/home-manager/home.nix
index 5fb5311b..8200975e 100644
--- a/.config/home-manager/home.nix
+++ b/.config/home-manager/home.nix
@@ -105,6 +105,10 @@
 
   programs.zoxide.enable = true;
 
+  # https://nixos.wiki/wiki/Home_Manager
+  #   - Prefer XDF_*
+  #   - If can't write the reason as a comment
+
   xdg.configFile."git/config".source = ../git/config;
   xdg.configFile."irb/irbrc".source = ../irb/irbrc;
   xdg.configFile."alacritty/alacritty.yml".source = ../alacritty/alacritty.yml;
@@ -115,6 +119,11 @@
   # Not under "starship/starship.toml"
   xdg.configFile."starship.toml".source = ../starship.toml;
 
+  # https://github.com/rbenv/rbenv-default-gems/issues/17
+  home.file.".default-gems".text = ''
+    irb-power_assert
+  '';
+
   home.packages = [
     pkgs.dprint
     pkgs.deno
diff --git a/home/.default-gems b/home/.default-gems
deleted file mode 100644
index 7a568778..00000000
--- a/home/.default-gems
+++ /dev/null
@@ -1 +0,0 @@
-irb-power_assert