Inelastic X-ray scattering (IXS) was used to study the Cu–O bond-stretching vibrations in the static stripe phase compound La1.48Nd0.4Sr0.12CuO4. It was found that the intrinsic width in Q-space of the previously reported huge anomalous phonon softening and broadening is approximately 0.08r.l.u. HWHM. A detailed comparison was also made to inelastic neutron scattering (INS) studies, which indicate a two-peak lineshape (with superimposed broad and narrow peaks) in the vicinity of the anomaly. The high resolution IXS data show that the narrow peak is mostly an artifact of the poor transverse Q-resolution of INS. Otherwise, the agreement between the INS and IXS was excellent.