diff --git a/absl/time/internal/cctz/src/time_zone_format.cc b/absl/time/internal/cctz/src/time_zone_format.cc
index 4c8d2f9cac7..b04c6e11616 100644
--- a/absl/time/internal/cctz/src/time_zone_format.cc
+++ b/absl/time/internal/cctz/src/time_zone_format.cc
@@ -22,6 +22,9 @@
 
 #if HAS_STRPTIME
 #if !defined(_XOPEN_SOURCE) && !defined(__FreeBSD__) && !defined(__OpenBSD__)
+#if defined(__APPLE__)
+#define _DARWIN_C_SOURCE
+#endif
 #define _XOPEN_SOURCE 500  // Exposes definitions for SUSv2 (UNIX 98).
 #endif
 #endif