Recent exoplanet studies have revealed that the orbital planes of planets are not always aligned with one another or with the equatorial plane of the central star. The misalignment has been ascribed to gravitational scattering by giant planets and/or companion stars(1-3) or to fly-bys in stellar cluster environments(4). Alternatively, the misalignment could be natal: that is, such planets were born in a warped protostellar disk(5,6). Warped disk structures have been reported in some transition disks and protoplanetary disks(7,8), but not in the earlier stages of protostar evolution, although such a possibility is suggested by outflow morphology(9,10). Here we report millimetre-wavelength dust continuum observations of the young embedded protostar IRAS 04368+2557 in the protostellar core L1527 at a distance(11) of 137 parsecs; the protostar's disk is almost edge-on(12-16). The inner and outer parts of the disk have slightly different orbital planes, connected at 40 to 60 astronomical units from the star, but the disk has point symmetry with respect to the position of the protostar. We interpret it as a warped disk that is rotationally supported. Because there is no evidence for a companion source(17,18), the warped structure must be due to either anisotropic accretion of gas with different rotational axes, or misalignment of the rotation axis of the disk with the magnetic field direction.