2 files changed, 9 insertions, 1 deletions
diff --git a/Library/Homebrew/resource.rb b/Library/Homebrew/resource.rb
index 922fbfa59..c7d73ffa7 100644
--- a/Library/Homebrew/resource.rb
+++ b/Library/Homebrew/resource.rb
@@ -99,8 +99,8 @@ class Resource
   def url val=nil, specs={}
     return @url if val.nil?
     @url = val
-    @using = specs.delete(:using)
     @specs.merge!(specs)
+    @using = @specs.delete(:using)
   end
 
   def version val=nil
diff --git a/Library/Homebrew/test/test_resource.rb b/Library/Homebrew/test/test_resource.rb
index a649ad142..50ebd4c0f 100644
--- a/Library/Homebrew/test/test_resource.rb
+++ b/Library/Homebrew/test/test_resource.rb
@@ -40,6 +40,14 @@ class ResourceTests < Test::Unit::TestCase
     assert_equal GitDownloadStrategy, @resource.download_strategy
   end
 
+  def test_does_not_mutate_specs_hash
+    specs = { :using => :git, :branch => 'master' }
+    @resource.url('foo', specs)
+    assert_equal({ :branch => 'master' }, @resource.specs)
+    assert_equal(:git, @resource.using)
+    assert_equal({ :using => :git, :branch => 'master' }, specs)
+  end
+
   def test_version
     @resource.version('1.0')
     assert_version_equal '1.0', @resource.version