A method of assembling a first panel and an essentially identical second panel by means of fastening devices for connecting the first and second panels to the supporting structure , wherein the fastening devices comprise a top portion , having a top surface , a bottom surface , a first edge portion and a second edge portion , a first leg and a second leg protruding downwardly from the bottom surface, wherein the first and second panel comprise a first edge groove and an opposite second edge groove , the first edge portion of the fastening devices being configured to be inserted into the first edge groove of the panels , and the second edge portion of the fastening devices being configured to be inserted into the second edge groove of the panels ; the first leg and the second leg being flexible and bendable towards each other; wherein the first leg comprises a first locking element and the second leg comprises a second locking element and wherein an upper surface of the supporting structure comprises an insertion groove comprising a first undercut groove and an opposite second undercut groove ; the method comprising the following steps: - connecting the first and second edge groove of the second panel to the supporting structure by one of said fastening devices , - displacing the first panel in a horizontal direction towards the already installed second panel until the first edge portion of the already installed fastening device is inserted into the second edge groove of the first panel , characterised in that it further comprises the following steps: - upward angling of the first panel to an angled position to enable insertion of the first edge portion of a further fastening device into the first edge groove of the first panel , - inserting the first edge portion of the further fastening device into the first edge groove of the first pane ; - downward angling of the first panel with the first edge portion of the further fastening device provided in the first edge groove against the upper surface of the supporting structure ; - pushing the first panel vertically downwards until the further fastening device has reached a locked position, wherein the first locking element of the further fastening device is snapped into the first undercut groove of the supporting structure and the second locking element of the further fastening device is snapped into the second undercut groove of the supporting structure to a locked position. - connecting the first and second edge groove of the second panel to the supporting structure by one of said fastening devices , - displacing the first panel in a horizontal direction towards the already installed second panel until the first edge portion of the already installed fastening device is inserted into the second edge groove of the first panel , - upward angling of the first panel to an angled position to enable insertion of the first edge portion of a further fastening device into the first edge groove of the first panel , - inserting the first edge portion of the further fastening device into the first edge groove of the first pane ; - downward angling of the first panel with the first edge portion of the further fastening device provided in the first edge groove against the upper surface of the supporting structure ; - pushing the first panel vertically downwards until the further fastening device has reached a locked position, wherein the first locking element of the further fastening device is snapped into the first undercut groove of the supporting structure and the second locking element of the further fastening device is snapped into the second undercut groove of the supporting structure to a locked position. <EOS>