We report on the experimental operation of a picosecond, singly resonant, synchronously pumped optical param etric oscillator (SPOPO) based on a $\mathrm{Zn}\mathrm{Ge}{\mathrm{P}}_2$ (ZGP) crystal. The ZGP SPOPO is pumped with the idler radiation from a diffraction-grating-tuned periodically poled lithium niobate SPOPO emitting a continuous picosecond pulse train ( $\Delta \tau \sim 8\mathrm{ps}$ , $f=76\mathrm{MHz}$ ). The noncritically $90°$ phase-matched ZGP SPOPO is tuned in the $3.8–5.6\mathrm{\mu m}$ range by tuning the pump wavelength ( $2.25–2.5\mathrm{\mu m}$ ). As high as $\sim 800\mathrm{mW}$ of average power is emitted at $4\mathrm{\mu m}$ .