1 files changed, 8 insertions, 0 deletions
diff --git a/utmpx.h b/utmpx.h
index 84e7b00..f4fadfd 100644
--- a/utmpx.h
+++ b/utmpx.h
@@ -32,6 +32,14 @@ SOFTWARE.
 #define _XOPEN_SOURCE 400
 #endif
 
+#if !defined __STDC_VERSION__ || __STDC_VERSION__ < 19901L
+#	if (defined _POSIX_C_SOURCE && _POSIX_C_SOURCE >= 200112L)
+#		error POSIX.1-2001 and later require a C99 compiler
+#	elif (defined _XOPEN_SOURCE && _XOPEN_SOURCE >= 600)
+#		error XOPEN Issue 6 and later require a C99 compiler
+#	endif
+#endif
+
 #if	(defined _XOPEN_SOURCE && ((defined _XOPEN_SOURCE_EXTENDED && _XOPEN_SOURCE_EXTENDED == 1) || 500 <= _XOPEN_SOURCE))
 /* ./src/utmpx/BOOT_TIME.c */
 #define BOOT_TIME /* TODO */