  We study the vacuum fluctuations of a massless scalar field $\hat{\Psi}$ on
the background of a global monopole. Due to the nontrivial topology of the
global monopole spacetime, characterized by a solid deficit angle parametrized
by $\eta^2$, we expect that $\left<\hat{\Psi}^2\right>_{\text{ren}}$ and
$\left<\hat{T}_{\mu\nu}\right>_{\text{ren}}$ are nonzero and proportional to
$\eta^2$, so that they annul in the Minkowski limit $\eta\to0$. However, due to
the naked singularity at the monopole core, the evolution of the scalar field
is not unique. In fact, they are in one to one correspondence with the boundary
conditions which turn into self-adjoint the spatial part of the wave operator.
We show that only Dirichlet boundary condition corresponds to our expectations
and gives zero contribution to the vacuum fluctuations in Minkowski limit. All
other boundary conditions give nonzero contributions in this limit due to the
nontrivial interaction between the field and the singularity.
