diff --git a/src/calibre/gui2/viewer/documentview.py b/src/calibre/gui2/viewer/documentview.py
index 632e082f33..4443e04f66 100644
--- a/src/calibre/gui2/viewer/documentview.py
+++ b/src/calibre/gui2/viewer/documentview.py
@@ -324,7 +324,7 @@ class Document(QWebPage):  # {{{
         if self.in_paged_mode:
             self.setPreferredContentsSize(QSize())
             self.switch_to_paged_mode(onresize=True)
-        self.javascript('window.mathjax.after_resize()')
+        self.javascript('if (window.mathjax) window.mathjax.after_resize();')
 
     def switch_to_fullscreen_mode(self):
         self.in_fullscreen_mode = True