diff --git a/src/calibre/gui2/viewer/documentview.py b/src/calibre/gui2/viewer/documentview.py
index f131dd522d..d5f881d4b4 100644
--- a/src/calibre/gui2/viewer/documentview.py
+++ b/src/calibre/gui2/viewer/documentview.py
@@ -188,6 +188,7 @@ class Document(QWebPage):
 
         # Miscellaneous
         settings.setAttribute(QWebSettings.LinksIncludedInFocusChain, True)
+        settings.setAttribute(QWebSettings.DeveloperExtrasEnabled, True)
         self.set_user_stylesheet()
         self.misc_config()