1 files changed, 5 insertions, 1 deletions

diff --git a/src/buffer.c b/src/buffer.c
index bf1b49e6ff4..fd2de4a2408 100644
--- a/src/buffer.c
+++ b/src/buffer.c
@@ -4669,7 +4669,11 @@ mmap_realloc (var, nbytes)
       else if (room - nbytes >= mmap_page_size)
         {
           /* Shrinking by at least a page.  Let's give some
-             memory back to the system.  */
+             memory back to the system.
+
+             The extra parens are to make the division happens first,
+             on positive values, so we know it will round towards
+             zero.  */
           mmap_enlarge (r, - ((room - nbytes) / mmap_page_size));
           result = *var;
           r->nbytes_specified = nbytes;