The P atom in the title compound, C15H18NO3P, is in a distorted tetra-hedral P(O)(O)2N environment; the bond angles at P are in the range 98.16 (6)-115.82 (6)°. In the crystal, adjacent mol-ecules are linked via N-H⋯O=P hydrogen bonds into a chain running parallel to the b axis. The methyl groups are disordered over two sets of sites in a 0.677 (14):0.323 (14) ratio. The crystal studied was a non-merohedral twin with a refined minor component of 22.31 (4)%.