diff --git a/Library/Homebrew/formula.rb b/Library/Homebrew/formula.rb
index 1c551aa254..8c68ad568b 100644
--- a/Library/Homebrew/formula.rb
+++ b/Library/Homebrew/formula.rb
@@ -7,7 +7,6 @@ require 'patches'
 require 'compilers'
 require 'build_environment'
 require 'build_options'
-require 'extend/set'
 
 
 class Formula
@@ -489,10 +488,8 @@ class Formula
   end
 
   # The full set of Requirements for this formula's dependency tree.
-  def recursive_requirements
-    reqs = ComparableSet.new
-    recursive_dependencies.each { |d| reqs.merge d.to_formula.requirements }
-    reqs.merge requirements
+  def recursive_requirements(&block)
+    Requirement.expand(self, &block)
   end
 
   def to_hash
diff --git a/Library/Homebrew/formula_installer.rb b/Library/Homebrew/formula_installer.rb
index 84a4a2cf59..ab021af0db 100644
--- a/Library/Homebrew/formula_installer.rb
+++ b/Library/Homebrew/formula_installer.rb
@@ -105,18 +105,14 @@ class FormulaInstaller
 
   def check_requirements
     unsatisfied = ARGV.filter_for_dependencies do
-      f.recursive_requirements.select do |req|
-        if req.satisfied?
-          false
+      f.recursive_requirements do |dependent, req|
+        if req.optional? || req.recommended?
+          Requirement.prune unless dependent.build.with?(req.name)
         elsif req.build?
-          not pour_bottle?
-        elsif req.optional? || req.recommended?
-          f.recursive_dependencies.map(&:to_formula).any? do |dep|
-            dep.build.with?(req.name)
-          end || f.build.with?(req.name)
-        else
-          true
+          Requirement.prune unless install_bottle?(dependent)
         end
+
+        Requirement.prune if req.satisfied?
       end
     end
 
diff --git a/Library/Homebrew/requirement.rb b/Library/Homebrew/requirement.rb
index 9b7d2ed8a4..d93d412f4b 100644
--- a/Library/Homebrew/requirement.rb
+++ b/Library/Homebrew/requirement.rb
@@ -106,4 +106,54 @@ class Requirement
       end
     end
   end
+
+  # Expand the requirements of dependent recursively, optionally yielding
+  # [dependent, req] pairs to allow callers to apply arbitrary filters to
+  # the list.
+  # The default filter, which is applied when a block is not given, omits
+  # optionals and recommendeds based on what the dependent has asked for.
+  def self.expand(dependent, &block)
+    reqs = ComparableSet.new
+
+    formulae = dependent.recursive_dependencies.map(&:to_formula)
+    formulae.unshift(dependent)
+
+    formulae.map(&:requirements).each do |requirements|
+      requirements.each do |req|
+        prune = catch(:prune) do
+          if block_given?
+            yield dependent, req
+          elsif req.optional? || req.recommended?
+            Requirement.prune unless dependent.build.with?(req.name)
+          end
+        end
+
+        next if prune
+
+        reqs << req
+      end
+    end
+
+    # We special case handling of X11Dependency and its subclasses to
+    # ensure the correct dependencies are present in the final list.
+    # If an X11Dependency is present after filtering, we eliminate
+    # all X11Dependency::Proxy objects from the list. If there aren't
+    # any X11Dependency objects, then we eliminate all but one of the
+    # proxy objects.
+    proxy = unless reqs.any? { |r| r.instance_of?(X11Dependency) }
+      reqs.find { |r| r.kind_of?(X11Dependency::Proxy) }
+    end
+
+    reqs.reject! do |r|
+      r.kind_of?(X11Dependency::Proxy)
+    end
+
+    reqs << proxy unless proxy.nil?
+    reqs
+  end
+
+  # Used to prune requirements when calling expand with a block.
+  def self.prune
+    throw(:prune, true)
+  end
 end
diff --git a/Library/Homebrew/requirements.rb b/Library/Homebrew/requirements.rb
index 1ef11dd5f0..7538079b05 100644
--- a/Library/Homebrew/requirements.rb
+++ b/Library/Homebrew/requirements.rb
@@ -1,4 +1,5 @@
 require 'requirement'
+require 'extend/set'
 
 # A dependency on a language-specific module.
 class LanguageModuleDependency < Requirement
diff --git a/Library/Homebrew/test/test_x11_deps.rb b/Library/Homebrew/test/test_x11_deps.rb
index c455d03d3c..433a2a1ab9 100644
--- a/Library/Homebrew/test/test_x11_deps.rb
+++ b/Library/Homebrew/test/test_x11_deps.rb
@@ -1,6 +1,5 @@
 require 'testing_env'
 require 'requirements'
-require 'extend/set'
 
 class X11DependencyTests < Test::Unit::TestCase
   def test_eql_instances_are_eql