  We use classical obstruction theory \`{a} la Eilenberg-Steenrod to obtain a
homotopy classification of $\mathrm{Spin}(7)$-structures on compact
$8$-manifolds with abelian fundamental group. As an application, we show that a
compact, connected Riemannian $8$-manifold with holonomy contained inside the
group $\mathrm{Spin}(7)$ has exactly two $\mathrm{Spin}(7)$-structures
extending the induced $G_{2}$-structure on the boundary.
