diff --git a/Library/Homebrew/build_environment.rb b/Library/Homebrew/build_environment.rb
index 6b4e7f0529..4f80b74adb 100644
--- a/Library/Homebrew/build_environment.rb
+++ b/Library/Homebrew/build_environment.rb
@@ -1,34 +1,44 @@
-# typed: false
+# typed: true
 # frozen_string_literal: true
 
 # Settings for the build environment.
 #
 # @api private
 class BuildEnvironment
+  extend T::Sig
+
+  sig { params(settings: Symbol).void }
   def initialize(*settings)
-    @settings = Set.new(*settings)
+    @settings = Set.new(settings)
   end
 
+  sig { params(args: T::Enumerable[Symbol]).returns(T.self_type) }
   def merge(*args)
     @settings.merge(*args)
     self
   end
 
+  sig { params(o: Symbol).returns(T.self_type) }
   def <<(o)
     @settings << o
     self
   end
 
+  sig { returns(T::Boolean) }
   def std?
     @settings.include? :std
   end
 
+  sig { returns(T::Boolean) }
   def userpaths?
     @settings.include? :userpaths
   end
 
   # DSL for specifying build environment settings.
   module DSL
+    extend T::Sig
+
+    sig { params(settings: Symbol).returns(BuildEnvironment) }
     def env(*settings)
       @env ||= BuildEnvironment.new
       @env.merge(settings)
@@ -50,16 +60,18 @@ class BuildEnvironment
   ].freeze
   private_constant :KEYS
 
+  sig { params(env: T.untyped).returns(T::Array[String]) }
   def self.keys(env)
     KEYS & env.keys
   end
 
+  sig { params(env: T.untyped, f: IO).void }
   def self.dump(env, f = $stdout)
     keys = self.keys(env)
     keys -= %w[CC CXX OBJC OBJCXX] if env["CC"] == env["HOMEBREW_CC"]
 
     keys.each do |key|
-      value = env[key]
+      value = env.fetch(key)
       s = +"#{key}: #{value}"
       case key
       when "CC", "CXX", "LD"
diff --git a/Library/Homebrew/cmd/--env.rb b/Library/Homebrew/cmd/--env.rb
index b4448f573e..a7eec71143 100644
--- a/Library/Homebrew/cmd/--env.rb
+++ b/Library/Homebrew/cmd/--env.rb
@@ -47,11 +47,10 @@ module Homebrew
       Utils::Shell.from_path(args.shell)
     end
 
-    env_keys = BuildEnvironment.keys(ENV)
     if shell.nil?
       BuildEnvironment.dump ENV
     else
-      env_keys.each do |key|
+      BuildEnvironment.keys(ENV).each do |key|
         puts Utils::Shell.export_value(key, ENV[key], shell)
       end
     end