This is arguable. It is necessary to understand that there were TWO movements of Proto-Indo-European language speakers, both in circular movements moving through Europe, the first time practically extinguishing the Anatolian farmers(1) and replacing them with the Beaker Culture, the second time(2) coming to rest in various geographies as Greek, Latin, Celtic, Slavic and German. These were among the Centum language portion of the Indo-European language family; the Satam languages, Iranian, Indo-Aryan and the Mitanni variation, stayed to the south and east of these Centum language loci.
(1) It is thought that the original population of Europe, probably largely Neanderthal, was added to by migrants from Anatolia, who brought with them the practice of agriculture. This mixed culture was then overwhelmed by the first incursion of the Indo-European speaking steppe dwellers from the East. The resultant Beaker Culture then receded as the steppe dwellers returned to the steppe, landing up finally in the Sintashta-Yamnaya complex, from which base the migrations westward starting again.
(2) This second time was when the westward migrations (and, for that matter, the Indo-Iranian migration, including the separate migration to Anatolia of the Mitanni) used the Sintashta-Yamnaya locations as a base and started from that.