diff --git a/activestorage/lib/active_storage/attached.rb b/activestorage/lib/active_storage/attached.rb
index 07e0d5c3ea..f11b62e744 100644
--- a/activestorage/lib/active_storage/attached.rb
+++ b/activestorage/lib/active_storage/attached.rb
@@ -17,7 +17,7 @@ module ActiveStorage
         case attachable
         when ActiveStorage::Blob
           attachable
-        when ActionDispatch::Http::UploadedFile
+        when ActionDispatch::Http::UploadedFile, Rack::Test::UploadedFile
           ActiveStorage::Blob.create_after_upload! \
             io: attachable.open,
             filename: attachable.original_filename,
diff --git a/activestorage/test/models/attachments_test.rb b/activestorage/test/models/attachments_test.rb
index 58af5dce6e..34cd62dcde 100644
--- a/activestorage/test/models/attachments_test.rb
+++ b/activestorage/test/models/attachments_test.rb
@@ -18,11 +18,17 @@ class ActiveStorage::AttachmentsTest < ActiveSupport::TestCase
     assert_equal "funky.jpg", @user.avatar.filename.to_s
   end
 
-  test "attach new blob" do
+  test "attach new blob from a Hash" do
     @user.avatar.attach io: StringIO.new("STUFF"), filename: "town.jpg", content_type: "image/jpg"
     assert_equal "town.jpg", @user.avatar.filename.to_s
   end
 
+  test "attach new blob from an UploadedFile" do
+    file = file_fixture "racecar.jpg"
+    @user.avatar.attach Rack::Test::UploadedFile.new file
+    assert_equal "racecar.jpg", @user.avatar.filename.to_s
+  end
+
   test "access underlying associations of new blob" do
     @user.avatar.attach create_blob(filename: "funky.jpg")
     assert_equal @user, @user.avatar_attachment.record