diff --git a/config/firefox/extensions.nix b/config/firefox/extensions.nix
index 00b6718..6347e7f 100644
--- a/config/firefox/extensions.nix
+++ b/config/firefox/extensions.nix
@@ -5,7 +5,7 @@ args:
     firefox-addons = args.firefox-addons or null;
   in
     if firefox-addons != null then
-      with firefox-addons.packages.${args.pkgs.system}; [
+      with firefox-addons.packages.${args.pkgs.stdenv.hostPlatform.system}; [
         ublock-origin
         vimium
         cookies-txt
diff --git a/modules/claude-code.nix b/modules/claude-code.nix
index d4cd5e5..5b93948 100644
--- a/modules/claude-code.nix
+++ b/modules/claude-code.nix
@@ -4,14 +4,14 @@ with lib;
 
 let
   # Detect system architecture and select appropriate package
-  claudePackage = if pkgs.system == "aarch64-darwin" then
+  claudePackage = if pkgs.stdenv.hostPlatform.system == "aarch64-darwin" then
     claude-code.packages.aarch64-darwin.claude-code
-  else if pkgs.system == "x86_64-linux" then
+  else if pkgs.stdenv.hostPlatform.system == "x86_64-linux" then
     claude-code.packages.x86_64-linux.claude-code
-  else if pkgs.system == "aarch64-linux" then
+  else if pkgs.stdenv.hostPlatform.system == "aarch64-linux" then
     claude-code.packages.aarch64-linux.claude-code
   else
-    throw "Unsupported system for Claude Code: ${pkgs.system}";
+    throw "Unsupported system for Claude Code: ${pkgs.stdenv.hostPlatform.system}";
 
   # Default global permissions
   defaultPermissions = {
diff --git a/modules/fonts.nix b/modules/fonts.nix
index 79e8419..386f084 100644
--- a/modules/fonts.nix
+++ b/modules/fonts.nix
@@ -23,7 +23,7 @@ in
     nerd-fonts.jetbrains-mono
 
     # Ubuntu font family
-    ubuntu_font_family
+    ubuntu-classic
 
     # CJK fonts for proper Chinese/Japanese/Korean character display
     noto-fonts-cjk-sans     # Comprehensive CJK support