1 files changed, 8 insertions, 0 deletions
diff --git a/wchar.h b/wchar.h
index 6c4d43d..934181f 100644
--- a/wchar.h
+++ b/wchar.h
@@ -27,6 +27,14 @@ OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
 SOFTWARE.
 */
 
+#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 __STDC_VERSION__ && 199409 <= __STDC_VERSION__)
 /* ./src/wchar/WCHAR_MAX.c */
 #define WCHAR_MAX                                                     (0x10FFFF)