diff --git a/src/config.h.in b/src/config.h.in
index 9507bb141..6ebc04c8a 100644
--- a/src/config.h.in
+++ b/src/config.h.in
@@ -28,3 +28,6 @@
 
 /* Define if you have the <sys/poll.h> header file */
 #undef HAVE_SYS_POLL_H
+
+/* Define if you have the `setvbuf' function. */
+#undef HAVE_SETVBUF