In one example, a fusing system for an additive manufacturing machine includes a warmer to preheat unfused build material in a work area, a dispenser to dispense a fusing agent on to build material in the work area in a pattern corresponding to an object slice, a fusing lamp to fuse patterned build material in the work area, a temperature sensor to measure a temperature of preheated unfused build material in the work area, and a controller operatively connected to the warmer and to the temperature sensor to adjust a heat output of the warmer to the work area based on a temperature measured by the temperature sensor.