A supplementary decision is intended to eliminate the incompleteness of the court decision passed in the case. It is derivative and, therefore, dependent on the decision of the court in the case, but regarding other issues it is autonomous (independent). The author criticizes formal explanations about the possibility of making a supplementary decision exclusively by the same court panel that made the decision on the case, as well as about returning the appeal along with the case to the court of first instance for making a supplementary decision. It is proposed to give the right to raise the issue of making a supplementary decision regarding the distribution of court costs for forensic examination carried out by experts and expert organizations on an equal basis with the court and the persons involved in the case, as well as equate the period for raising this issue with the time limit for appealing the court decision. The author contends the impossibility of presenting new (additional) evidence when the court considers the issue of making a supplementary decision, as well as the impossibility of restoring the procedural period missed for the delivery of this issue. It was revealed that a supplementary decision can also be made in the case when the resolution of a particular issue by virtue of the law is mandatory for the court. The author determines alternative ways for completing the court decision on the case, if the possibility of making a supplementary decision is lost. Attention is drawn to the ambiguity of the assessment given to the supplementary decision as a mechanism for replenishing the court decision in the case due to its objectively inherent shortcomings