diff --git a/TODO.org b/TODO.org
index 1b677505..71b78b90 100644
--- a/TODO.org
+++ b/TODO.org
@@ -738,6 +738,9 @@ One spelling for one operation; != stays, and not= is refused with a suggestion
 of !=.
 
 * Checker
+** TODO Checking a wide fold of let operands is slow
+A 2000-operand (bit-and (let …) …) takes 32 s to check (37 s before the bit operators);
+2000 plain names take 0.03 s. Something per operand is quadratic or worse.
 
 ** DONE A dyn value takes .field and [:key]
 CLOSED: [2026-09-26]