BMW has issued a recall on the 2016-2017 S1000RR and the 2017 S1000R because of a potential loose bolt in the rear suspension system. The recall affects 21 units in total in the U.S.

According to documents released by the National Highway Traffic Safety Administration, one of the bolts on the rear shock’s deflection lever could come loose, affecting the handling of the motorcycle. The problem may be affecting either the bolt connecting the lever to the rear shock or the one connecting the lever to the swingarm. One of these two bolts may not have been tightened to specifications. Should one of the bolts come loose, riders may notice a knocking sound coming from the rear suspension.

BMW first became aware of this issue in December 2016 following an internal quality report from its assembly plant. BMW analyzed its production records and identified motorcycles that may have this problem. On Dec. 20, BMW initiated recall proceedings.

Dealers will replace the applicable bolted connection and ensure the bolts are tightened to specification. The recall affects 20 units of the S1000RR and a single unit of the S1000R.