The observation of mating between species of different genera in field conditions is extremely rare. Here, we report an instance of heterospecific copulation between a male of the Nagy’s mountain grasshopper ( Pseudopodisma nagyi ) and a female of the green mountain grasshopper ( Miramella alpina ), which was observed in subalpine grasslands in the Veľká Fatra Mountains in central Slovakia. After being transferred to the laboratory, the female laid egg pods. This finding supports the hypothesis that the two species are closely related and suggests the need for a taxonomic revision within the tribe Podismini. If it occurs more often, reproductive interference may impact the viability of populations of both the green mountain grasshopper and Nagy’s mountain grasshopper populations wherever they are in contact. Further data are needed to test whether reproductive interference reduces the viability of their syntopic populations.