diff --git a/CHANGELOG.md b/CHANGELOG.md
index 009490656..cfc2e0053 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -9,6 +9,8 @@
   when the `:html5` is set to `true` [@volmer](https://github.com/volmer)
 
 ### bug fix
+  * Collection input that uses automatic collection translation properly sets checked values.
+  Closes [#971](https://github.com/plataformatec/simple_form/issues/971) [@nashby](https://github.com/nashby)
   * Collection input generates `required` attribute if it has `prompt` option. [@nashby](https://github.com/nashby)
 
 ## 3.0.1
diff --git a/lib/simple_form/inputs/collection_input.rb b/lib/simple_form/inputs/collection_input.rb
index 3fc298506..2b1eae56b 100644
--- a/lib/simple_form/inputs/collection_input.rb
+++ b/lib/simple_form/inputs/collection_input.rb
@@ -90,7 +90,7 @@ def collection_includes_basic_objects?(collection_classes)
       def translate_collection
         if translated_collection = translate(:options)
           @collection = collection.map do |key|
-            [translated_collection[key] || key, key]
+            [translated_collection[key] || key, key.to_s]
           end
           true
         end
diff --git a/test/inputs/collection_check_boxes_input_test.rb b/test/inputs/collection_check_boxes_input_test.rb
index 6254d1a3a..41552cf28 100644
--- a/test/inputs/collection_check_boxes_input_test.rb
+++ b/test/inputs/collection_check_boxes_input_test.rb
@@ -53,6 +53,20 @@ class CollectionCheckBoxesInputTest < ActionView::TestCase
     end
   end
 
+  test 'input that uses automatic collection translation for check_boxes should properly set checked values' do
+    store_translations(:en, simple_form: { options: { defaults: {
+      gender: { male: 'Male', female: 'Female'}
+    } } } ) do
+      @user.gender = 'male'
+
+      with_input_for @user, :gender, :check_boxes, collection: [:male, :female]
+      assert_select 'input[type=checkbox][value=male][checked=checked]'
+      assert_select 'input[type=checkbox][value=female]'
+      assert_select 'label.collection_check_boxes', 'Male'
+      assert_select 'label.collection_check_boxes', 'Female'
+    end
+  end
+
   test 'input check boxes does not wrap the collection by default' do
     with_input_for @user, :active, :check_boxes