diff --git a/bignum.c b/bignum.c
index c0847e620d..bf234dba6a 100644
--- a/bignum.c
+++ b/bignum.c
@@ -6691,6 +6691,12 @@ rb_big_abs(VALUE x)
     return x;
 }
 
+int
+rb_big_sign(VALUE x)
+{
+    return BIGNUM_SIGN(x);
+}
+
 size_t
 rb_big_size(VALUE big)
 {
diff --git a/include/ruby/ruby.h b/include/ruby/ruby.h
index eeae2f6879..72e91c2f7b 100644
--- a/include/ruby/ruby.h
+++ b/include/ruby/ruby.h
@@ -1185,9 +1185,10 @@ void *rb_check_typeddata(VALUE, const rb_data_type_t *);
 #define RSTRUCT_SET(st, idx, v) rb_struct_aset(st, INT2NUM(idx), (v))
 #define RSTRUCT_GET(st, idx)    rb_struct_aref(st, INT2NUM(idx))
 
-#define RBIGNUM_SIGN(b) (RB_FIX2LONG(rb_big_cmp((b), RB_INT2FIX(0))) >= 0)
-#define RBIGNUM_POSITIVE_P(b) (RB_FIX2LONG(rb_big_cmp((b), RB_INT2FIX(0))) >= 0)
-#define RBIGNUM_NEGATIVE_P(b) (RB_FIX2LONG(rb_big_cmp((b), RB_INT2FIX(0))) < 0)
+int rb_big_sign(VALUE);
+#define RBIGNUM_SIGN(b) (rb_big_sign(b))
+#define RBIGNUM_POSITIVE_P(b) (RBIGNUM_SIGN(b)!=0)
+#define RBIGNUM_NEGATIVE_P(b) (RBIGNUM_SIGN(b)==0)
 
 #define R_CAST(st)   (struct st*)
 #define RBASIC(obj)  (R_CAST(RBasic)(obj))