diff --git a/actionpack/lib/action_view/helpers/asset_tag_helper.rb b/actionpack/lib/action_view/helpers/asset_tag_helper.rb
index f6abea38eddbc..a32beb610075b 100644
--- a/actionpack/lib/action_view/helpers/asset_tag_helper.rb
+++ b/actionpack/lib/action_view/helpers/asset_tag_helper.rb
@@ -516,7 +516,8 @@ def self.cache_asset_timestamps=(value)
         def compute_public_path(source, dir, ext = nil, include_host = true)
           has_request = @controller.respond_to?(:request)
 
-          if ext && (File.extname(source).blank? || File.exist?(File.join(ASSETS_DIR, dir, "#{source}.#{ext}")))
+          source_ext = File.extname(source)[1..-1]
+          if ext && (source_ext.blank? || (ext != source_ext && File.exist?(File.join(ASSETS_DIR, dir, "#{source}.#{ext}"))))
             source += ".#{ext}"
           end