A bale shape monitoring system for a round baler for detecting a misshapen bale during bale formation. The system includes a pair of spaced apart rollers mounted to a movable member located within the bale-forming chamber, and which are normally engaged with spaced apart baler belts when the bale has a uniform diameter in the vicinity of the rollers. A rotation sensing arrangement detects the rotation of the rollers, caused by engagement of the rollers with the belts during normal bale formation. In the event the bale is formed with a lesser diameter in the vicinity of one of the rollers, the associated belt moves out of contact with the roller, and the lack of roller rotation is sensed so as to provide a signal to the operator to steer the baler to supply crop material to the lesser diameter area of the bale. Once a uniform diameter is again obtained, both rollers continue to rotate so as to indicate to the operator that the bale has a uniform diameter.