A method and a knitting machine for producing a knitted product composed of fiber material fed by a roller pair (11c) are described. The stitches are formed as usual by knitting elements (3) being raised out of a non-knitting position into a fiber take-up position, while at the same time previously formed stitches are being knocked over, and being withdrawn again after the fiber material (6) is inserted. The presence of fiber material is monitored by means of a sensor (22), which when there is no fiber material present emits an error signal, as a result of which the knitting elements are prevented from being raised further into the fiber take-up position. According to the invention, when the error signal occurs, the knitting elements (3) are withdrawn from an intermediate position again without the previously formed stitches being knocked over and without the fiber material being taken up. In addition, the sensor is preferably arranged at a location between the roller pair (11c) and the knitting system (4) (FIG. 1).