In error-prone communications, packet loss results in missing information of shape, motion and texture of a video object (VO). Error concealment refers to the recovery of lost information at the decoder. In this paper, we propose a spatial shape error concealment technique. We consider a geometric representation of the shape of a VO consisting of its boundary, which can be extracted from the received α-plane. Some boundary parts are missing due to errors. We propose a method for modeling the received boundary based on a shape-preserving approximation that uses T-splines. Such an approximation provides a good estimation of the direction of a missing boundary segment, which we use to construct a concealment spline that joins smoothly with the received boundary parts.