diff --git a/bn_mp_set_double.c b/bn_mp_set_double.c
--- a/bn_mp_set_double.c
+++ b/bn_mp_set_double.c
@@ -2,9 +2,9 @@
 #ifdef BN_MP_SET_DOUBLE_C
 /* LibTomMath, multiple-precision integer library -- Tom St Denis */
 /* SPDX-License-Identifier: Unlicense */
 
-#if defined(__STDC_IEC_559__) || defined(__GCC_IEC_559)
+#if defined(__STDC_IEC_559__) || defined(__GCC_IEC_559) || defined(_MSC_VER)
 mp_err mp_set_double(mp_int *a, double b)
 {
    uint64_t frac;
    int exp;