diff --git a/bignum.c b/bignum.c
index 4b926160f5..fb95412164 100644
--- a/bignum.c
+++ b/bignum.c
@@ -40,7 +40,8 @@ static VALUE big_three = Qnil;
 #endif
 #define ALIGNOF(type) ((int)offsetof(struct { char f1; type f2; }, f2))
 /* (sizeof(d) * CHAR_BIT <= (n) ? 0 : (n)) is same as n but suppress a warning, C4293, by Visual Studio.  */
-#define LSHIFTX(d, n) (sizeof(d) * CHAR_BIT <= (n) ? 0 : ((d) << (sizeof(d) * CHAR_BIT <= (n) ? 0 : (n))))
+#define LSHIFTABLE(d, n) ((n) < sizeof(d) * CHAR_BIT)
+#define LSHIFTX(d, n) (!LSHIFTABLE(d, n) ? 0 : ((d) << (!LSHIFTABLE(d, n) ? 0 : (n))))
 #define CLEAR_LOWBITS(d, numbits) ((d) & LSHIFTX(~((d)*0), (numbits)))
 #define FILL_LOWBITS(d, numbits) ((d) | (LSHIFTX(((d)*0+1), (numbits))-1))
 #define POW2_P(x) (((x)&((x)-1))==0)