Let V be a complete discrete valuation ring of mixed characteristic (0,3) in which 3 is a uniformizer, and put A=V[[x,y]]/(3+x2−y3)
Nearby in the stack
. We construct a nonzero class
a∈K2(A;Z/3)
whose restriction to the fraction field of
A
is zero. Thus Gersten injectivity for algebraic
K
-theory with
Z/3
-coefficients fails for a two-dimensional ramified regular local ring. The coefficient Bockstein of
a
is zero, while the map
K2(A)→K2(F)
is injective. We also indicate the expected analogous construction for every odd prime. This counterexample does not contradict the integral Gersten conjecture but it rules out a naive reduction to finite coefficients.