For any function
f
f
belonging to
Q
p
,
λ
Q^{p,\lambda }
, a certain proper subspace of the classical Morrey space
L
p
,
λ
L^{p, \lambda }
, a sharp capacity weak-type estimate is obtained for its Riesz potential
I
α
f
I_{\alpha } f
. This extends a 1969 result due to Franco Conti.