The spiral structure of the single crystal MnSi has been studied by SANS near T_C=29K in the magnetic field. When the field (H>20 mT) is applied along one of the 〈1 1 1〉 axes, it produces a single domain sample with the helix wave vector along the field. The 90°-reorientation of the spin spiral from the [1 1 1] axis to [1 -1 0] axis is observed in the field range from 130 to 180 mT in close vicinity to T_C. Further increase of the field above H=180 mT, restores the original orientation of the helix and leads to the induced ferromagnetic state at H=350 mT. The SANS experiments demonstrate that not a new phase, but helix reorientation occurs in the narrow domain of the H-T phase diagram near T_C.