Index: lib/acts_as_cached/fragment_cache.rb
===================================================================
--- lib/acts_as_cached/fragment_cache.rb	(revision 7306)
+++ lib/acts_as_cached/fragment_cache.rb	(revision 7308)
@@ -62,7 +62,7 @@
           cache = controller.read_fragment(action_cache_path.path)
           if cache && (conditional || conditional.nil?)
             controller.rendered_action_cache = true
-            set_content_type!(action_cache_path)
+            set_content_type!(action_cache_path, action_cache_path.extension)
             controller.send(:render_text, cache)
             false
           else