diff --git a/src/calibre/gui2/viewer/javascript.py b/src/calibre/gui2/viewer/javascript.py
index b9584562c3..108266454a 100644
--- a/src/calibre/gui2/viewer/javascript.py
+++ b/src/calibre/gui2/viewer/javascript.py
@@ -80,7 +80,7 @@ class JavaScriptLoader(object):
             evaljs(src)
 
         if not lang:
-            lang = 'en'
+            lang = default_lang or 'en'
 
         def lang_name(l):
             l = l.lower()