diff --git a/lib/i18n.rb b/lib/i18n.rb
index 3ce75181..418bd0fc 100755
--- a/lib/i18n.rb
+++ b/lib/i18n.rb
@@ -141,7 +141,7 @@ def reload!
     # always return the same translations/values per unique combination of argument
     # values.
     def translate(*args)
-      options  = args.last.is_a?(Hash) ? args.pop : {}
+      options  = args.last.is_a?(Hash) ? args.pop.dup : {}
       key      = args.shift
       backend  = config.backend
       locale   = options.delete(:locale) || config.locale
@@ -219,7 +219,7 @@ def translate!(key, options={})
     #     I18n.transliterate("Jürgen", :locale => :en) # => "Jurgen"
     #     I18n.transliterate("Jürgen", :locale => :de) # => "Juergen"
     def transliterate(*args)
-      options      = args.pop if args.last.is_a?(Hash)
+      options      = args.pop.dup if args.last.is_a?(Hash)
       key          = args.shift
       locale       = options && options.delete(:locale) || config.locale
       handling     = options && (options.delete(:throw) && :throw || options.delete(:raise) && :raise)
@@ -230,7 +230,8 @@ def transliterate(*args)
     end
 
     # Localizes certain objects, such as dates and numbers to local formatting.
-    def localize(object, options = {})
+    def localize(object, options = nil)
+      options = options ? options.dup : {}
       locale = options.delete(:locale) || config.locale
       format = options.delete(:format) || :default
       config.backend.localize(locale, object, format, options)
diff --git a/lib/i18n/tests/localization/date.rb b/lib/i18n/tests/localization/date.rb
index a866f90c..a7234752 100644
--- a/lib/i18n/tests/localization/date.rb
+++ b/lib/i18n/tests/localization/date.rb
@@ -44,6 +44,13 @@ def setup
           assert_nothing_raised { I18n.l(@date, :format => '%x') }
         end
 
+        test "localize Date: does not modify the options hash" do
+          options = { :format => '%b', :locale => :de }
+          assert_equal 'Mar', I18n.l(@date, options)
+          assert_equal({ :format => '%b', :locale => :de }, options)
+          assert_nothing_raised { I18n.l(@date, options.freeze) }
+        end
+
         test "localize Date: given nil it raises I18n::ArgumentError" do
           assert_raise(I18n::ArgumentError) { I18n.l(nil) }
         end
diff --git a/lib/i18n/tests/lookup.rb b/lib/i18n/tests/lookup.rb
index 63c21ac8..62c069d1 100644
--- a/lib/i18n/tests/lookup.rb
+++ b/lib/i18n/tests/lookup.rb
@@ -41,6 +41,13 @@ def setup
         assert_nothing_raised { I18n.t(:foo, :locale => :xx) }
       end
 
+      test "lookup: does not modify the options hash" do
+        options = {}
+        assert_equal "a", I18n.t(:string, options)
+        assert_equal({}, options)
+        assert_nothing_raised { I18n.t(:string, options.freeze) }
+      end
+
       test "lookup: given an array of keys it translates all of them" do
         assert_equal %w(bar baz), I18n.t([:bar, :baz], :scope => [:foo])
       end