We describe a new snake species of the genus Tachymenoides from the scientifically unexplored southern sector of the Otishi National Park in Peru (Region Junín). The single adult male specimen with a total length of 407 mm was obtained in the Pantano la Esperanza swamp of a puna valley at 3248 m a.s.l. The new species has smooth dorsal scales without apical pits in 19/17/15 series, 1 preocular, 2 postoculars, 1 loreal, undivided nasal scale, 2+3 temporals, 139 ventrals, 55 subcaudals, and a divided cloacal scale. In life, the dorsum is pale yellowish brown with scattered black blotches that form a paravertebral stripe (one scale wide) on each side at the posterior half of the body. The flanks are black ventrolaterally (2–3 scales high), followed at the posterior half of the body by a pale yellowish-brown longitudinal stripe of two scales width, bordered dorso­laterally by the black paravertebral stripe. The throat and first 60 mm of the ventral body are pale yellowish tan with black flecks, and a ventrolateral black stripe on each side of the same length, the remaining venter and tail entirely black. The head has dorsally a black stripe from the posterior margins of the postoculars extending over the outside margins of the rostrals over the head scales (2–3 scales in width) and narrowing to 1 scale width on the neck region before ending; laterally, the head has black flecks on the supralabials, and a black stripe extending from postoculars diagonally over parietals over posterior su­pralabials to the corner of the jaw. The iris is copper with a vertical pupil. The type locality of Proctoporus titans is corrected.