Loading psf fits files in Siril pixel math

Pixel math drop down file manager does not show PSF fits files in listing to load. Is this by design, or do I have some setting off? Thanks ahead for answer.

Are you sure this is FITS file and not tiff fil

You are absolutely right. and I checked this before posting cause its a special note in the deconvolution doc: PSF are stored as tif. I must have been seeing/reading extensions backwards. Sorry to waste your time, Ill convert them. thanks