diff --git a/src/hb-unicode-private.hh b/src/hb-unicode-private.hh
index 519fa0b..ddba1ac 100644
--- a/src/hb-unicode-private.hh
+++ b/src/hb-unicode-private.hh
@@ -149,7 +149,8 @@
 	  (ch >= 0x202A && ch <= 0x202E) ||
 	  (ch >= 0x2060 && ch <= 0x2063) ||
 	  (ch == 0x2028)
-	 )) || unlikely (ch == 0x00AD
+	 )) || unlikely (ch == 0x0009
+		      || ch == 0x00AD
 		      || ch == 0x034F
 		      || ch == 0xFEFF);
 }