diff -urN a/ext/tidy/tidy.c b/ext/tidy/tidy.c
--- a/ext/tidy/tidy.c   2019-01-09 10:54:13.000000000 +0100
+++ b/ext/tidy/tidy.c   2021-10-05 11:15:04.381237541 +0200
@@ -31,7 +31,7 @@
 #include "ext/standard/info.h"

 #include "tidy.h"
-#include "buffio.h"
+#include "tidybuffio.h"

 /* compatibility with older versions of libtidy */
 #ifndef TIDY_CALL