diff --git a/Gemfile b/Gemfile
index ea0c930..f5a0384 100644
--- a/Gemfile
+++ b/Gemfile
@@ -6,7 +6,7 @@ source "https://rubygems.org"
 gem "nanoc", "~> 4.12"
 
 ##
-# nanoc filters
+# filters
 gem "nanoc-gzip.rb"
 gem "nanoc-webpack.rb"
 gem "nanoc-tidy.rb"
@@ -14,16 +14,9 @@ gem "rainpress", "~> 1.0"
 gem "sass", "~> 3.7"
 
 ##
-# Web server
+# dev
 gem "server.rb"
-
-##
-# Other
 gem "ryo.rb"
-gem "test-cmd.rb"
-gem "lockf.rb"
 gem "standard", "~> 1.24"
 gem "paint", "~> 2.3"
-gem "dotenv", "~> 2.8"
 gem "listen", "~> 3.0"
-gem "memoize", "~> 1.3"
diff --git a/Gemfile.lock b/Gemfile.lock
index fedef0a..5a5c919 100644
--- a/Gemfile.lock
+++ b/Gemfile.lock
@@ -12,7 +12,6 @@ GEM
     ddmetrics (1.1.0)
     ddplugin (1.0.3)
     diff-lcs (1.5.1)
-    dotenv (2.8.1)
     ffi (1.16.3)
     immutable-ruby (0.1.0)
       concurrent-ruby (~> 1.1)
@@ -24,9 +23,7 @@ GEM
     listen (3.9.0)
       rb-fsevent (~> 0.10, >= 0.10.3)
       rb-inotify (~> 0.9, >= 0.9.10)
-    lockf.rb (0.13.0)
     memo_wise (1.8.0)
-    memoize (1.3.1)
     method_source (1.0.0)
     nanoc (4.12.20)
       addressable (~> 2.5)
@@ -138,7 +135,6 @@ GEM
       lint_roller (~> 1.1)
       rubocop-performance (~> 1.20.2)
     stringio (3.1.0)
-    test-cmd.rb (0.6.0)
     tty-color (0.6.0)
     tty-command (0.10.1)
       pastel (~> 0.8)
@@ -152,10 +148,7 @@ PLATFORMS
   ruby
 
 DEPENDENCIES
-  dotenv (~> 2.8)
   listen (~> 3.0)
-  lockf.rb
-  memoize (~> 1.3)
   nanoc (~> 4.12)
   nanoc-gzip.rb
   nanoc-tidy.rb
@@ -166,7 +159,6 @@ DEPENDENCIES
   sass (~> 3.7)
   server.rb
   standard (~> 1.24)
-  test-cmd.rb
 
 BUNDLED WITH
    2.5.9
diff --git a/nanoc/lib/mixin.rb b/nanoc/lib/mixin.rb
index 560d502..2551a8a 100644
--- a/nanoc/lib/mixin.rb
+++ b/nanoc/lib/mixin.rb
@@ -1,9 +1,6 @@
 # frozen_string_literal: true
 
 module Mixin
-  require "memoize"
-  extend Memoize
-
   require_relative "mixin/t"
   require_relative "mixin/inline"
   require_relative "mixin/erb"
@@ -17,10 +14,11 @@ module Mixin
   end
 
   def build_dir
-    nanoc = Ryo.from YAML.load_file(File.join(Dir.getwd, "nanoc.yaml"))
-    nanoc.output_dir
+    @build_dir ||= begin
+      nanoc = Ryo.from YAML.load_file(File.join(Dir.getwd, "nanoc.yaml"))
+      nanoc.output_dir
+    end
   end
-  memoize :build_dir
 
   include T
   include Inline