diff --git a/src/random_mars.cpp b/src/random_mars.cpp
index 2f935c92c2..36fd2b4bc8 100644
--- a/src/random_mars.cpp
+++ b/src/random_mars.cpp
@@ -184,7 +184,7 @@ void RanMars::select_subset(bigint ntarget, int nmine, int *mark, int *next)
   int active[2],first[2],last[2];
   int newactive[2],newfirst[2],newlast[2];
   bigint nmark,nflipall;
-  bigint activeall[2],bsum[4],bsumall[4];
+  bigint activeall[2],bsum[3],bsumall[3];
   double thresh;
 
   active[0] = nmine;