diff --git a/src/calibre/debug.py b/src/calibre/debug.py
index 5384e28b7c..7814af5d9d 100644
--- a/src/calibre/debug.py
+++ b/src/calibre/debug.py
@@ -219,7 +219,7 @@ def main(args=sys.argv):
         run_debug_gui(opts.gui_debug)
     elif opts.viewer:
         from calibre.gui2.viewer.main import main
-        main(['ebook-viewer'] + args[1:])
+        main(['ebook-viewer', '--debug-javascript'] + args[1:])
     elif opts.py_console:
         from calibre.utils.pyconsole.main import main
         main()