We show that weak antilocalization by disorder competes with
resonant Andreev reflection from a Majorana zero mode to produce a zerovoltage
conductance peak of order e^2/h in a superconducting nanowire. The
phase conjugation needed for quantum interference to survive a disorder
average is provided by particle–hole symmetry—in the absence of timereversal
symmetry and without requiring a topologically nontrivial phase. We
identify methods of distinguishing the Majorana resonance from the weak
antilocalization effect.