1 files changed, 8 insertions, 0 deletions
diff --git a/sched.h b/sched.h
index 1d60ba8..cdc251f 100644
--- a/sched.h
+++ b/sched.h
@@ -48,6 +48,14 @@ SOFTWARE.
 #	define _POSIX_SOURCE
 #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 _POSIX_C_SOURCE && 199309 <= _POSIX_C_SOURCE)
 /* ./src/sched/SCHED_FIFO.c */
 #define SCHED_FIFO                                                           (0)