diff --git a/lib/simple_form/core_ext/hash.rb b/lib/simple_form/core_ext/hash.rb
new file mode 100644
index 00000000..18ca8bef
--- /dev/null
+++ b/lib/simple_form/core_ext/hash.rb
@@ -0,0 +1,16 @@
+# TODO: Delete this file when we drop support for Rails 3.0
+#   This method is already implemented in active_support 3.1
+
+unless Hash.new.respond_to?(:deep_dup)
+  class Hash
+    # Returns a deep copy of hash.
+    def deep_dup
+      duplicate = self.dup
+      duplicate.each_pair do |k,v|
+        tv = duplicate[k]
+        duplicate[k] = tv.is_a?(Hash) && v.is_a?(Hash) ? tv.deep_dup : v
+      end
+      duplicate
+    end
+  end
+end
diff --git a/lib/simple_form/form_builder.rb b/lib/simple_form/form_builder.rb
index 8c1a314d..5af1d92f 100644
--- a/lib/simple_form/form_builder.rb
+++ b/lib/simple_form/form_builder.rb
@@ -1,3 +1,5 @@
+require 'simple_form/core_ext/hash'
+
 module SimpleForm
   class FormBuilder < ActionView::Helpers::FormBuilder
     attr_reader :template, :object_name, :object, :wrapper
@@ -98,7 +100,7 @@ module SimpleForm
     # given SimpleForm.time_zone_priority and SimpleForm.country_priority are used respectivelly.
     #
     def input(attribute_name, options={}, &block)
-      options = @defaults.deep_merge(options) if @defaults
+      options = @defaults.deep_dup.deep_merge(options) if @defaults
 
       chosen =
         if name = options[:wrapper]
diff --git a/test/form_builder/general_test.rb b/test/form_builder/general_test.rb
index 017175ff..8386a6db 100644
--- a/test/form_builder/general_test.rb
+++ b/test/form_builder/general_test.rb
@@ -287,6 +287,16 @@ class FormBuilderTest < ActionView::TestCase
     assert_select 'input.default_class#specific_id'
   end
 
+  test 'builder should receive a default argument and pass it to the inputs without changing the defaults' do
+    with_concat_form_for @user, :defaults => { :input_html => { :class => 'default_class', :id => 'default_id' } } do |f|
+      concat(f.input :name)
+      concat(f.input :credit_limit)
+    end
+
+    assert_select "input.string.default_class[name='user[name]']"
+    assert_no_select "input.string[name='user[credit_limit]']"
+  end
+
   # WITHOUT OBJECT
   test 'builder should generate properly when object is not present' do
     with_form_for :project, :name