diff --git a/mrbgems/mruby-bigint/core/bigint.c b/mrbgems/mruby-bigint/core/bigint.c
index 3ead06c61..6da7b73b4 100644
--- a/mrbgems/mruby-bigint/core/bigint.c
+++ b/mrbgems/mruby-bigint/core/bigint.c
@@ -465,6 +465,7 @@ udiv(mrb_state *mrb, mpz_t *qq, mpz_t *rr, mpz_t *xx, mpz_t *yy)
     q.p[j] = qhat;
     if (j == 0) break;
   }
+  x.sz = yy->sz;
   urshift(mrb, rr, &x, ns);
   trim(&q);
   mpz_set(mrb, qq, &q);