diff --git a/TODO b/TODO
index b0eac7a69..d763c30c5 100644
--- a/TODO
+++ b/TODO
@@ -1,6 +1,9 @@
 General fixes:
 =============
 
+- Warn at compile time (and runtime with HB_DEBUG?) if no Unicode funcs
+  found / set.
+
 - In hb_shape(), assert if direction is INVALID.
 
 - Fix TT 'kern' on/off and GPOS interaction (move kerning before GPOS).