diff --git a/tzfile.h b/tzfile.h
index 51fac7a..87f419c 100644
--- a/tzfile.h
+++ b/tzfile.h
@@ -117,3 +117,11 @@ struct tzhead {
 */
 
 #define isleap(y) (((y) % 4) == 0 && ((y) % 100) != 0 || ((y) % 400) == 0)
+
+#ifdef __STDC__
+#define MODERN
+#endif /* defined __STDC__ */
+
+#ifdef __TURBOC__
+#define MODERN
+#endif /* defined __TURBOC__ */