How to fix ob_end_flush() error?

I also had this issue with wordpress and couldn’t properly resolve it. Ended up with this filthy hack to prevent the error from showing:

// Get the current error reporting level
$e_level = error_reporting();

// Turn off error reporting
error_reporting(0);

ob_start();
echo 'This is a horrible hack';
$buffer_contents = ob_get_clean();
ob_end_flush();

// Reset error reporting level to previous
error_reporting($e_level);

Everything does seem to work as expected, however I’m not proud of it!