Petar may have had to also face the incursions of the Magyars, who had been defeated and forced into Pannonia by his father in 896.

Perhaps after an initial defeat, Petar had come to terms with the enemy and now uses Magyar groups as his allies against Serbia.

Various Magyar clans and chieftains appear to have begun to settle in what was still Bulgarian territory north of the Danube, where they may have become Bulgarian federates, enjoying independence from the Árpád dynasty.

This arrangement paves the way for the eventual loss of the region to the Magyars, although that will happen over the half-century following Petar's death.

Petar apparently allows these groups to cross Bulgaria and raid imperial territories in Thrace and Macedonia, perhaps as an underhanded reaction against Constantinople’s support for the Serbian rebellion.