The phase diagram of the Mn&sngbnd;Bi system near the compound MnBi was studied with single crystals in the as‐grown and heat‐treated states. The results show that the high‐temperature phase of MnBi is in fact a separate compound with chemical formula Mn1.08Bi, when grown from a Bi‐rich solution. It was found that the transformation of MnBi at 355°C upon heating is associated with a peritectic decomposition of MnBi into Mn1.08Bi+liquid, and the transformation at 340°C upon cooling of the high‐temperature phase is the result of decomposition of Mn1.08Bi to MnBi±Mn.