Described is a device for securing a length-measurement device (4) in place on a guide rail (1) for a carriage (2) which moves along the rail. The device has a scale (4) and a sensor head (3) which can move relative to the scale, the sensor head (3) being detachably mounted on the carriage (2). The scale (4) is detachably coupled, by means of positively interlocking parts, directly (or indirectly via a carrier (5) attached to the scale), directly to recesses (8; 9) in the guide rail (1), the longitudinal edges of the scale (4) or scale carrier (5) being inserted into the matching recesses (8; 9) in the rail (1).