1 files changed, 8 insertions, 0 deletions
diff --git a/unctrl.h b/unctrl.h
index 34ddcbf..e068fe7 100644
--- a/unctrl.h
+++ b/unctrl.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 _XOPEN_SOURCE)
 /* src/curses/chtype.c */
 #ifndef __TYPE_chtype_DEFINED__