How To Get Undo And Redo To Appear In Custom QAT Tool Bar

I am trying to create a custom QAT toolbar. Everything works except for the Undo and Redo buttons. They're giving me an error:

The specified control type 'button' is incompatible with the actual control type 'gallery' ID: Undo
The specified control type 'button' is incompatible with the actual control type 'gallery' ID: Redo

Code:
<customUI xmlns=http://schemas.microsoft.com/office/2009/2007/customui onLoad="OnRibbonLoad">
<ribbon startFromScratch="true">
<qat>
<documentControls>
<button idMso ="Copy"/>
<button idMso ="Paste"/>
<button idMso ="PrintDialogAccess"/>

[code]...

"OnRibbonLoad" is a function in a module that just opens and closes a dummy form.If I take the Undo and Redo lines out of this code, it works fine. No errors.