Why PSP_PREMATURE flag on a property page gives me a compiler error ?

Hi !,

I have a property sheet, and I want all the pages created at the creation of the property sheet, so I use ( for the first page):

GetPage(1)->m_psp.dwFlags |= PSP_PREMATURE;

But the compiler says me: error C2065: 'PSP_PREMATURE' : undeclared identifier


Why ?, Is there any way to solve this ? ( I'm using 5.0 version).

Thanks, Bye !
Braulio