diff --git a/addons/web/controllers/main.py b/addons/web/controllers/main.py
index 64df4a95ecf..c0117043b43 100644
--- a/addons/web/controllers/main.py
+++ b/addons/web/controllers/main.py
@@ -282,7 +282,7 @@ def concat_files(file_list, reader=None, intersperse=""):
     if reader is None:
         def reader(f):
             import codecs
-            with codecs.open(f, 'r', "utf-8-sig") as fp:
+            with codecs.open(f, 'rb', "utf-8-sig") as fp:
                 return fp.read().encode("utf-8")
 
     files_content = []