Fire crews from three towns were called to a burning stable block in Denby on Friday night.
The stable workshop and around 60 bales of hay were reported alight at around 8.20pm.
Firefighters from Ripley, Heanor and Belper attended the blaze off Church Street.
They used two hose reel jets and one mainline jet to extinguish the flames.
Police are treating the blaze as arson.