diff --git a/src/time_zone_format.cc b/src/time_zone_format.cc
index 7ecfec4..f34b7bc 100644
--- a/src/time_zone_format.cc
+++ b/src/time_zone_format.cc
@@ -21,7 +21,8 @@
 #endif
 
 #if HAS_STRPTIME
-# if !defined(_XOPEN_SOURCE) && !defined(__FreeBSD__) && !defined(__OpenBSD__)
+# if !defined(_XOPEN_SOURCE) && !defined(__FreeBSD__) && !defined(__OpenBSD__) && \
+     !defined(__APPLE__)
 #  define _XOPEN_SOURCE 500  // Exposes definitions for SUSv2 (UNIX 98).
 # endif
 #endif