--- a/mail/base/content/messageWindow.xhtml
+++ b/mail/base/content/messageWindow.xhtml
@@ -48,16 +48,24 @@
 %bondOpenPGPDTD;
 #endif
 <!ENTITY % quickFilterBarDTD SYSTEM "chrome://messenger/locale/quickFilterBar.dtd">
 %quickFilterBarDTD;
 <!ENTITY % msgViewPickerDTD SYSTEM "chrome://messenger/locale/msgViewPickerOverlay.dtd" >
 %msgViewPickerDTD;
 <!ENTITY % lightningDTD SYSTEM "chrome://lightning/locale/lightning.dtd">
 %lightningDTD;
+<!ENTITY % calendarDTD SYSTEM "chrome://calendar/locale/calendar.dtd" >
+%calendarDTD;
+<!ENTITY % calendarMenuOverlayDTD SYSTEM "chrome://calendar/locale/menuOverlay.dtd" >
+%calendarMenuOverlayDTD;
+<!ENTITY % toolbarDTD SYSTEM "chrome://lightning/locale/lightning-toolbar.dtd">
+%toolbarDTD;
+<!ENTITY % eventDialogDTD SYSTEM "chrome://calendar/locale/calendar-event-dialog.dtd" >
+%eventDialogDTD;
 ]>
 
 <!--
   - This window displays a single message.
   -->
 <window id="messengerWindow"
         xmlns="http://www.mozilla.org/keymaster/gatekeeper/there.is.only.xul"
         xmlns:html="http://www.w3.org/1999/xhtml"