diff --git a/profiles/osapi/modern.h b/profiles/osapi/modern.h
index e4d6a00..710eb54 100644
--- a/profiles/osapi/modern.h
+++ b/profiles/osapi/modern.h
@@ -1,6 +1,10 @@
 #ifndef PY_OSAPI_MODERN_H
 #define PY_OSAPI_MODERN_H
 
+#ifndef _XOPEN_SOURCE
+#define _XOPEN_SOURCE                   700
+#endif
+
 /* atomics */
 #ifdef  __ATOMIC_ACQUIRE
 #define HAVE_BUILTIN_ATOMIC             1
@@ -343,7 +347,6 @@
 #define _NETBSD_SOURCE                  1
 #define _POSIX_C_SOURCE                 200809L
 #define _REENTRANT                      1
-#define _XOPEN_SOURCE                   700
 #define _XOPEN_SOURCE_EXTENDED          1
 #define __BSD_VISIBLE                   1
 #define __EXTENSIONS__                  1