diff --git a/mrbgems/mruby-bigint/core/bigint.c b/mrbgems/mruby-bigint/core/bigint.c
index 5d91c0673..b8dc4487b 100644
--- a/mrbgems/mruby-bigint/core/bigint.c
+++ b/mrbgems/mruby-bigint/core/bigint.c
@@ -90,6 +90,8 @@ static size_t
 digits(mpz_t *x)
 {
   size_t i;
+
+  if (x->sz == 0) return 0;
   for (i = (x->sz) - 1; (x->p)[i] == 0 ; i--)
     if (i == 0) break;
   return i+1;