diff --git a/scheme/base.sld b/scheme/base.sld
index 136c493f..51890350 100644
--- a/scheme/base.sld
+++ b/scheme/base.sld
@@ -1047,6 +1047,10 @@
     " Cyc_check_num(data, num);
       if (obj_is_int(num)) {
         return_closcall1(data, k, obj_int2obj( abs( obj_obj2int(num))));
+      } else if (is_object_type(num) && type_of(num) == bignum_tag){
+        alloc_bignum(data, bn);
+        mp_abs(&bignum_value(num), &bignum_value(bn));
+        return_closcall1(data, k, bn);
       } else {
         make_double(d, fabs(((double_type *)num)->value));
         return_closcall1(data, k, &d);