diff --git a/lib/delayed_attachment_fu.rb b/lib/delayed_attachment_fu.rb
index 5193245..87ffbf8 100644
--- a/lib/delayed_attachment_fu.rb
+++ b/lib/delayed_attachment_fu.rb
@@ -4,7 +4,7 @@ module DelayedAttachmentFu
     def delay_attachment_fu_thumbnails
       include DelayedAttachmentFu::InstanceMethods
       after_create do |file|
-        if file.image?
+        if file.thumbnailable?
           Delayed::Job.enqueue CreateThumbnailsJob.new(file.class.name, file.id)
         end
       end
diff --git a/test/unit/image_test.rb b/test/unit/image_test.rb
index b29a651..8357b30 100644
--- a/test/unit/image_test.rb
+++ b/test/unit/image_test.rb
@@ -84,4 +84,14 @@ class ImageTest < Test::Unit::TestCase
     end
   end
 
+  should 'not create a background job for an image that is already a thumbnail' do
+    # this test verifies whether it created background jobs also for the
+    # thumbnails!
+    assert_no_difference Delayed::Job, :count do
+      image = Image.new(:owner => profile, :uploaded_data => fixture_file_upload('/files/rails.png', 'image/png'))
+      image.stubs(:is_thumbnail?).returns(true)
+      image.save!
+    end
+  end
+
 end
--
libgit2 0.21.2