The present invention relates to a packaging machine which seals a cover-film at a tray, which has been previously filled with a packaging item, whereas the packaging machine comprises an upper tool and a lower tool which are pressed together during the sealing of the cover-film to the tray, and which comprises means to detect misalignment of the packaging item in the tray, a misaligned tray in the lower tool and/or a foreign object between the upper and the lower tool prior to and/or during the sealing of the cover film to the tray.