diff --git a/lib/fcntl.in.h b/lib/fcntl.in.h
index fd7520e..dea7449 100644
--- a/lib/fcntl.in.h
+++ b/lib/fcntl.in.h
@@ -70,6 +70,10 @@ extern void _gl_register_fd (int fd, const char *filename);
 
 /* Fix up the O_* macros.  */
 
+#ifndef O_CIO
+# define O_CIO 0
+#endif
+
 #if !defined O_DIRECT && defined O_DIRECTIO
 /* Tru64 spells it `O_DIRECTIO'.  */
 # define O_DIRECT O_DIRECTIO