  We present accurate new wavenumbers for a set of 13 mid-infrared
fine-structure lines. The wavenumbers were determined from observations of the
planetary nebula NGC 7027 and of the red supergiant Alpha Scorpii. Most of the
new wavenumbers are good to within 0.0025%, or 8 km/s. We provide details on
the measurements and present an analysis of the errors. In addition, we present
the first observations of hyperfine splitting in the [Na IV] 1106 cm-1 line.
