diff --git a/Library/Homebrew/utils.rb b/Library/Homebrew/utils.rb
index a1a40e95f9..ae6ca50b9e 100644
--- a/Library/Homebrew/utils.rb
+++ b/Library/Homebrew/utils.rb
@@ -181,9 +181,9 @@ module HomebrewInreplaceExtension
   # Looks for Makefile style variable defintions and replaces the
   # value with "new_value", or removes the definition entirely.
   # See inreplace in utils.rb
-  def change_make_var! flag, new_value
-    new_value = "#{flag}=#{new_value}" unless new_value.to_s.empty?
-    gsub! Regexp.new("^#{flag}\\s*=.*$"), new_value.to_s
+  def change_make_var! flag, new_value=nil
+    new_value = "#{flag}=#{new_value}" unless new_value == nil
+    gsub! Regexp.new("^#{flag}\\s*=\\s*(.*)$"), new_value
   end
   def remove_make_var! flags
     flags.each { |flag| change_make_var! flag, "" }