We report the frequency stabilization of a cw extended-cavity diode laser against saturated absorption lines of the ${\mathrm{H}}_2{}^{17}\mathrm{O}$ isotopologue of water vapor at around $1.384\mu \mathrm{m}$ . The saturation of rotovibrational transitions is achieved by filling a high-finesse optical resonator with ${\mathrm{H}}_2{}^{17}\mathrm{O}$ at low pressure and by locking the laser frequency to the resonator by using the Pound–Drever–Hall technique. Absolute frequency stabilization is obtained, locking the cavity resonance to the center of the sub-Doppler line by means of the wavelength modulation method. A relative frequency stability of ${\sigma }_y\left(\tau \right)={10}^{-13}{(0.1{\tau }^{-2}+0.9)}^{1∕2}$ is demonstrated for integration times in the range $4\mathrm{ms}<\tau <30\mathrm{s}$ .