diff --git a/bignum.c b/bignum.c
index d2c1e865c7..a02f4c4d99 100644
--- a/bignum.c
+++ b/bignum.c
@@ -3799,7 +3799,7 @@ bigdivrem(VALUE x, VALUE y, volatile VALUE *divp, volatile VALUE *modp)
     dd = nlz(q);
     q <<= dd;
     if (dd) {
-        tds = ALLOCV_N(BDIGIT, tmpy, RBIGNUM_LEN(y));
+        tds = ALLOCV_N(BDIGIT, tmpy, ny);
 	j = 0;
 	t2 = 0;
 	while (j<ny) {