diff --git a/Library/Homebrew/download_strategy.rb b/Library/Homebrew/download_strategy.rb
index 0a09045623..80631d86c2 100644
--- a/Library/Homebrew/download_strategy.rb
+++ b/Library/Homebrew/download_strategy.rb
@@ -8,6 +8,7 @@ class AbstractDownloadStrategy
   end
 
   def expand_safe_system_args args
+    args = args.dup
     args.each_with_index do |arg, ii|
       if arg.is_a? Hash
         unless ARGV.verbose?
@@ -20,7 +21,7 @@ class AbstractDownloadStrategy
     end
     # 2 as default because commands are eg. svn up, git pull
     args.insert(2, '-q') unless ARGV.verbose?
-    return args
+    args
   end
 
   def quiet_safe_system *args
diff --git a/Library/Homebrew/test/test_download_strategies.rb b/Library/Homebrew/test/test_download_strategies.rb
index 13392272b9..fcef2a2821 100644
--- a/Library/Homebrew/test/test_download_strategies.rb
+++ b/Library/Homebrew/test/test_download_strategies.rb
@@ -1,6 +1,42 @@
 require 'testing_env'
 require 'download_strategy'
 require 'bottles' # XXX: hoist these regexps into constants in Pathname?
+require 'hardware' # XXX: wat. fix this require mess!
+
+class SoftwareSpecDouble
+  attr_reader :url, :specs
+
+  def initialize(url="http://foo.com/bar.tar.gz", specs={})
+    @url = url
+    @specs = specs
+  end
+end
+
+class AbstractDownloadStrategyTests < Test::Unit::TestCase
+  def setup
+    @name = "foo"
+    @package = SoftwareSpecDouble.new
+    @strategy = AbstractDownloadStrategy.new(@name, @package)
+    @args = %w{foo bar baz}
+  end
+
+  def test_expand_safe_system_args_with_explicit_quiet_flag
+    @args << { :quiet_flag => '--flag' }
+    expanded_args = @strategy.expand_safe_system_args(@args)
+    assert_equal %w{foo bar baz --flag}, expanded_args
+  end
+
+  def test_expand_safe_system_args_with_implicit_quiet_flag
+    expanded_args = @strategy.expand_safe_system_args(@args)
+    assert_equal %w{foo bar -q baz}, expanded_args
+  end
+
+  def test_expand_safe_system_args_does_not_mutate_argument
+    result = @strategy.expand_safe_system_args(@args)
+    assert_equal %w{foo bar baz}, @args
+    assert_not_same @args, result
+  end
+end
 
 class DownloadStrategyDetectorTests < Test::Unit::TestCase
   def setup