diff --git a/opt/bignum.c b/opt/bignum.c
index d0b1d66d..11b619ad 100644
--- a/opt/bignum.c
+++ b/opt/bignum.c
@@ -1163,7 +1163,7 @@ sexp sexp_mul (sexp ctx, sexp a, sexp b) {
       r = sexp_make_fixnum(prod);
     break;
   case SEXP_NUM_FIX_FLO:
-    r = sexp_make_flonum(ctx, sexp_fixnum_to_double(a)*sexp_flonum_value(b));
+    r = (a==SEXP_ZERO ? a : sexp_make_flonum(ctx, sexp_fixnum_to_double(a)*sexp_flonum_value(b)));
     break;
   case SEXP_NUM_FIX_BIG:
     r = sexp_bignum_fxmul(ctx, NULL, b, sexp_unbox_fixnum(sexp_fx_abs(a)), 0);