diff --git a/Library/Homebrew/build.rb b/Library/Homebrew/build.rb
index e59b5be6aa..96245f0223 100755
--- a/Library/Homebrew/build.rb
+++ b/Library/Homebrew/build.rb
@@ -59,8 +59,10 @@ class Build
 
   def initialize(f)
     @f = f
+    # Expand requirements before dependencies, as requirements
+    # may add dependencies if a default formula is activated.
+    @reqs = expand_reqs
     @deps = expand_deps
-    @reqs = f.recursive_requirements
   end
 
   def post_superenv_hacks
@@ -77,6 +79,19 @@ class Build
       not ARGV.include? '--env=super'
   end
 
+  def expand_reqs
+    f.recursive_requirements do |dependent, req|
+      if (req.optional? || req.recommended?) && dependent.build.without?(req.name)
+        Requirement.prune
+      elsif req.build? && dependent != f
+        Requirement.prune
+      elsif req.satisfied? && req.default_formula? && (dep = req.to_dependency).installed?
+        dependent.deps << dep
+        Requirement.prune
+      end
+    end
+  end
+
   def expand_deps
     f.recursive_dependencies do |dependent, dep|
       if dep.optional? || dep.recommended?
@@ -84,18 +99,18 @@ class Build
       elsif dep.build?
         Dependency.prune unless dependent == f
       end
-    end.map(&:to_formula)
+    end
   end
 
   def install
-    keg_only_deps = deps.select(&:keg_only?)
+    keg_only_deps = deps.map(&:to_formula).select(&:keg_only?)
 
     pre_superenv_hacks
     require 'superenv'
 
     deps.each do |dep|
       opt = HOMEBREW_PREFIX/:opt/dep
-      fixopt(dep) unless opt.directory? or ARGV.ignore_deps?
+      fixopt(dep.to_formula) unless opt.directory? or ARGV.ignore_deps?
     end
 
     if superenv?
@@ -105,9 +120,11 @@ class Build
       ENV.setup_build_environment
       post_superenv_hacks
       reqs.each(&:modify_build_environment)
+      deps.each(&:modify_build_environment)
     else
       ENV.setup_build_environment
       reqs.each(&:modify_build_environment)
+      deps.each(&:modify_build_environment)
 
       keg_only_deps.each do |dep|
         opt = dep.opt_prefix
diff --git a/Library/Homebrew/dependency.rb b/Library/Homebrew/dependency.rb
index a6905bc37e..91def84422 100644
--- a/Library/Homebrew/dependency.rb
+++ b/Library/Homebrew/dependency.rb
@@ -5,6 +5,7 @@ class Dependency
   include Dependable
 
   attr_reader :name, :tags
+  attr_accessor :env_proc
 
   def initialize(name, tags=[])
     @name = name
@@ -54,6 +55,10 @@ class Dependency
     tags << 'universal' if to_formula.build.has_option? 'universal'
   end
 
+  def modify_build_environment
+    env_proc.call unless env_proc.nil?
+  end
+
   class << self
     # Expand the dependencies of dependent recursively, optionally yielding
     # [dependent, dep] pairs to allow callers to apply arbitrary filters to
diff --git a/Library/Homebrew/formula_installer.rb b/Library/Homebrew/formula_installer.rb
index fa7578c4f5..3c6dd46068 100644
--- a/Library/Homebrew/formula_installer.rb
+++ b/Library/Homebrew/formula_installer.rb
@@ -120,13 +120,16 @@ class FormulaInstaller
   def check_requirements
     unsatisfied = ARGV.filter_for_dependencies do
       f.recursive_requirements do |dependent, req|
-        if req.optional? || req.recommended?
-          Requirement.prune unless dependent.build.with?(req.name)
-        elsif req.build?
-          Requirement.prune if install_bottle?(dependent)
+        if (req.optional? || req.recommended?) && dependent.build.without?(req.name)
+          Requirement.prune
+        elsif req.build? && install_bottle?(dependent)
+          Requirement.prune
+        elsif req.satisfied?
+          Requirement.prune
+        elsif req.default_formula?
+          dependent.deps << req.to_dependency
+          Requirement.prune
         end
-
-        Requirement.prune if req.satisfied?
       end
     end
 
diff --git a/Library/Homebrew/requirement.rb b/Library/Homebrew/requirement.rb
index a5e9367422..dcacf45e0b 100644
--- a/Library/Homebrew/requirement.rb
+++ b/Library/Homebrew/requirement.rb
@@ -1,4 +1,5 @@
 require 'dependable'
+require 'dependency'
 require 'build_environment'
 
 # A base class for non-formula requirements needed by formulae.
@@ -36,6 +37,10 @@ class Requirement
     self.class.fatal || false
   end
 
+  def default_formula?
+    self.class.default_formula || false
+  end
+
   # Overriding #modify_build_environment is deprecated.
   # Pass a block to the the env DSL method instead.
   def modify_build_environment
@@ -54,6 +59,14 @@ class Requirement
     [name, *tags].hash
   end
 
+  def to_dependency
+    f = self.class.default_formula
+    raise "No default formula defined for #{inspect}" if f.nil?
+    dep = Dependency.new(f, tags)
+    dep.env_proc = method(:modify_build_environment)
+    dep
+  end
+
   private
 
   def infer_name
@@ -136,11 +149,6 @@ class Requirement
         requirements.each do |req|
           if prune?(dependent, req, &block)
             next
-          # TODO: Do this in a cleaner way, perhaps with another type of
-          # dependency type.
-          elsif req.class.default_formula
-            dependent.class.depends_on(req.class.default_formula)
-            next
           else
             reqs << req
           end
diff --git a/Library/Homebrew/test/test_requirement.rb b/Library/Homebrew/test/test_requirement.rb
index ccf137e4d2..5d89defb05 100644
--- a/Library/Homebrew/test/test_requirement.rb
+++ b/Library/Homebrew/test/test_requirement.rb
@@ -96,4 +96,28 @@ class RequirementTests < Test::Unit::TestCase
   ensure
     klass.send(:remove_const, const) if klass.const_defined?(const)
   end
+
+  def test_dsl_default_formula
+    req = Class.new(Requirement) { default_formula 'foo' }.new
+    assert req.default_formula?
+  end
+
+  def test_to_dependency
+    req = Class.new(Requirement) { default_formula 'foo' }.new
+    assert_equal Dependency.new('foo'), req.to_dependency
+  end
+
+  def test_to_dependency_calls_requirement_modify_build_environment
+    error = Class.new(StandardError)
+
+    req = Class.new(Requirement) do
+      default_formula 'foo'
+      satisfy { true }
+      env { raise error }
+    end.new
+
+    assert_raises(error) do
+      req.to_dependency.modify_build_environment
+    end
+  end
 end