diff --git a/mailnews/base/resources/content/messageWindow.xul b/mailnews/base/resources/content/messageWindow.xul
index f1d37fa20f27..fa8039053c45 100644
--- a/mailnews/base/resources/content/messageWindow.xul
+++ b/mailnews/base/resources/content/messageWindow.xul
@@ -41,7 +41,7 @@ Rights Reserved.
 		align="vertical"
         width="750"
         height="500"
-        persist="width height screenX screenY"
+        persist="width height screenX screenY sizemode"
 		windowtype="mail:messageWindow">