[support] template.php function called from a php block

I wrote a very basic function in template.php. When I edit a page and switch the input format to PHP, the preview works fine and I see the result of the function call. However, when I save the page, I get:

Fatal error: Call to undefined function: phptemplate_1() in .../includes/common.inc(1342) : eval()'d code on line 32

This is my test function in template.php:

function phptemplate_1() { $output = '<h1>Doh!</h1>';

return $output; }

And there is only this on my page:

<?php print phptemplate_1(); ?>

If I write the function in node.tpl.php, it works. If I write the code in a page and preview it, it works. When I save the page, it doesn't.

I'm pretty sure this is a newbie mistake, include missing maybe? I've been reading about it, browsing but I couldn't find anything specific. Any pointers?

Thanks.