The HfFe 6 Ge 6 -type YMn 6 Sn 6 - x In x compounds (x=0.03, 0.10, 0.23, 0.37, 0.72) have been studied by means of magnetization measurements and powder neutron diffraction studies. YMn 6 Sn 5 . 9 7 In 0 . 0 3 and YMn 6 Sn 5 . 9 0 In 0 . 1 0 display helimagnetic order over their entire ordered temperature range (T N =330 and 334 K, respectively). YMn 6 Sn 5 . 7 7 In 0 . 2 3 and YMn 6 Sn 5 . 6 3 In 0 . 3 7 order ferromagnetically (T c =324 and 323 K, respectively) and undergo a ferro- to helimagnetic transition below T t =308 and 258 K. YMn 6 Sn 5 . 2 8 In 0 . 7 2 displays ferromagnetic order over its entire ordered temperature range (T c =312 K). In the helimagnetic state, unusual thermal variations of the q z component of the propagating vector were observed with Δq z /ΔT>0 for x=0.03 and 0.10 and Δq z /ΔT<0 for x=0.23 and 0.37.