1. A method of authenticating a finger of a user against a stored template and expanding the stored template, comprising the steps of: acquiring a present partial candidate fingerprint image; retrieving a stored enrolment representation for said user, the stored enrolment representation comprising said stored template, and a stored representation of at least a first previous partial candidate fingerprint image acquired in connection with a previous failed authentication attempt for said user; determining if a first match between a representation of the present partial candidate fingerprint image and said stored template fulfills a first template updating requirement; determining if a second match between said representation of the present partial candidate fingerprint image and said stored representation of the at least first previous partial candidate fingerprint image fulfills a second template updating requirement; when it is determined that said first match fulfills said first template updating requirement and said second match fulfills said second template updating requirement: providing a signal indicating a successful authentication; and forming a first expanded template based on said stored template, said present partial candidate fingerprint image and said at least first previous partial candidate fingerprint image.