Don't do fractions if buffer is ASCII-only
diff --git a/src/hb-ot-layout-private.hh b/src/hb-ot-layout-private.hh
index 60fca26..049b232 100644
--- a/src/hb-ot-layout-private.hh
+++ b/src/hb-ot-layout-private.hh
@@ -249,6 +249,7 @@
 
   if (u >= 0x80)
   {
+    buffer->scratch_flags |= HB_BUFFER_SCRATCH_FLAG_HAS_NON_ASCII;
     if (unlikely (unicode->is_default_ignorable (u)))
     {
       buffer->scratch_flags |= HB_BUFFER_SCRATCH_FLAG_HAS_DEFAULT_IGNORABLES;