  Majorana bound states are zero-energy modes localized at the ends of a
one-dimensional (1D) topological superconductor. Introducing disorder usually
increases the Majorana localization length, until eventually inducing a
topological phase transition to a trivial phase. In this work we show that in
some cases weak disorder causes the Majorana localization length to decrease,
making the topological phase more robust. Increasing the disorder further
eventually leads to a change of trend and to a phase transition to a trivial
phase. Interestingly the transition occurs at $\xi_0\gg l$, where $l$ is the
disorder mean-free path and $\xi_0$ is the localization length in the clean
limit. Our results are particularly relevant to a 1D topological
superconductors formed in planar Josephson junctions.
