1 files changed, 9 insertions, 1 deletions

diff --git a/src/lib/libc/include/namespace.h b/src/lib/libc/include/namespace.h
index b42c00e4a1..8503de47be 100644
--- a/src/lib/libc/include/namespace.h
+++ b/src/lib/libc/include/namespace.h
@@ -1,4 +1,4 @@
-/*      $OpenBSD: namespace.h,v 1.15 2019/11/25 22:57:28 guenther Exp $ */
+/*      $OpenBSD: namespace.h,v 1.16 2023/10/29 14:26:13 millert Exp $  */
 
 #ifndef _LIBC_NAMESPACE_H_
 #define _LIBC_NAMESPACE_H_
@@ -20,6 +20,14 @@
  */
 
 /*
+ * ISO C11 or higher is required to build libc.
+ * This must come _before_ sys/cdefs.h is included.
+ */
+#if !defined(__STDC_VERSION__) || __STDC_VERSION__ < 201112
+#define _ISOC11_SOURCE 1
+#endif
+
+/*
  * For explanations of how to use these, see README
  * For explanations of why we use them and how they work, see DETAILS
  */