diff --git a/Code/Mantid/MantidQt/MantidWidgets/inc/MantidQtMantidWidgets/MWDiag.ui b/Code/Mantid/MantidQt/MantidWidgets/inc/MantidQtMantidWidgets/MWDiag.ui
index 203629bde9d64996cdc310d18f33fb3497573e61..df662ce8cdd5c13e2809ab8f006db81337b22937 100644
--- a/Code/Mantid/MantidQt/MantidWidgets/inc/MantidQtMantidWidgets/MWDiag.ui
+++ b/Code/Mantid/MantidQt/MantidWidgets/inc/MantidQtMantidWidgets/MWDiag.ui
@@ -246,6 +246,9 @@
         <property name="multipleFiles" stdset="0" >
          <bool>false</bool>
         </property>
+        <property name="optional" stdset="0" >
+         <bool>true</bool>
+        </property>
        </widget>
       </item>
       <item>