diff --git a/Library/Homebrew/requirement.rb b/Library/Homebrew/requirement.rb
index f8a6f056bf..a5e9367422 100644
--- a/Library/Homebrew/requirement.rb
+++ b/Library/Homebrew/requirement.rb
@@ -120,60 +120,64 @@ class Requirement
     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
+  class << self
+    # 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 expand(dependent, &block)
+      reqs = ComparableSet.new
 
-    formulae = dependent.recursive_dependencies.map(&:to_formula)
-    formulae.unshift(dependent)
+      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)
+      formulae.map(&:requirements).each do |requirements|
+        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
         end
+      end
 
-        next if prune
+      # 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
 
-        # TODO: Do this in a cleaner way, perhaps with another type of
-        # dependency type.
-        if req.class.default_formula
-          dependent.class.depends_on(req.class.default_formula)
-          next
+      reqs.reject! do |r|
+        r.kind_of?(X11Dependency::Proxy)
+      end
+
+      reqs << proxy unless proxy.nil?
+      reqs
+    end
+
+    def prune?(dependent, req, &block)
+      catch(:prune) do
+        if block_given?
+          yield dependent, req
+        elsif req.optional? || req.recommended?
+          prune unless dependent.build.with?(req.name)
         end
-
-        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) }
+    # Used to prune requirements when calling expand with a block.
+    def prune
+      throw(:prune, true)
     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