diff --git a/src/time_zone_format.cc b/src/time_zone_format.cc
index a5e7c8c..44e5696 100644
--- a/src/time_zone_format.cc
+++ b/src/time_zone_format.cc
@@ -20,7 +20,11 @@
 
 #if defined(HAS_STRPTIME) && HAS_STRPTIME
 # if !defined(_XOPEN_SOURCE) && !defined(__FreeBSD__) && !defined(__OpenBSD__)
-#  define _XOPEN_SOURCE 500  // Exposes definitions for SUSv2 (UNIX 98).
+#  if defined(__QNX__)
+#    define _XOPEN_SOURCE 600  // Exposes definitions for QNX 7.1.
+#  else
+#    define _XOPEN_SOURCE 500  // Exposes definitions for SUSv2 (UNIX 98).
+#  endif
 # endif
 #endif