function_exists('dynamic_sidebar') is false

I have:

<?php if ( !function_exists('dynamic_sidebar') || !dynamic_sidebar() ) : ?>
<-----code that shows up----->
	<!--
	is_active? <?php is_active_sidebar(1); ?>
	is_dynamic? <?php is_dynamic_sidebar(1); ?>
	dynamic exists? <?php function_exists('dynamic_sidebar'); ?>
	-->
<?php endif; ?>

For some reason, the function_exists call is returning false. Since this is in a standard include file, and I’m not overwriting it, I don’t see why this function wouldn’t exist. Is there a step I need to take to enable dynamic sidebars or to have wp-includes\widgets.php included?

Note: I do have a register_sidebar call in my functions.php