diff --git a/lib/responders/http_cache_responder.rb b/lib/responders/http_cache_responder.rb
index 1285baf..3599db2 100644
--- a/lib/responders/http_cache_responder.rb
+++ b/lib/responders/http_cache_responder.rb
@@ -20,8 +20,7 @@ def to_format
           resource.updated_at.utc if resource.respond_to?(:updated_at)
         end.compact.max
 
-        controller.response.last_modified = timestamp
-
+        controller.response.last_modified = timestamp if timestamp
         if request.fresh?(controller.response)
           head :not_modified
           return
diff --git a/test/http_cache_responder_test.rb b/test/http_cache_responder_test.rb
index d34381e..d3c55ee 100644
--- a/test/http_cache_responder_test.rb
+++ b/test/http_cache_responder_test.rb
@@ -16,6 +16,10 @@ def single
   def collection
     respond_with [Model.new(Time.utc(2009)), Model.new(Time.utc(2008))]
   end
+
+  def empty
+    respond_with []
+  end
 end
 
 class HttpCacheResponderTest < ActionController::TestCase
@@ -90,4 +94,11 @@ def test_collection_chooses_the_latest_timestamp
     assert_match /xml/, @response.body
     assert_equal 200, @response.status
   end
+
+  def test_work_with_an_empty_array
+    get :empty
+    assert_nil @response.headers["Last-Modified"]
+    assert_match /xml/, @response.body
+    assert_equal 200, @response.status
+  end
 end
\ No newline at end of file