1 files changed, 8 insertions, 0 deletions
diff --git a/regexp.h b/regexp.h
index ee4ae29..322db1a 100644
--- a/regexp.h
+++ b/regexp.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 && _XOPEN_SOURCE < 600)
 /* ./src/regexp/loc1.c */
 extern char *loc1;