diff --git a/TODO b/TODO
index dbcb20991bf0a7629f17db494ca075ad8edd3987..5c8c18774630c7a24dc6a0577484a81d33ffaf37 100644
--- a/TODO
+++ b/TODO
@@ -101,3 +101,7 @@ Roughly in order of importance.                                     -*-org-*-
 
 * Speed up kwant.contrib.digest
   by using SipHash and Ziggurat algorithm in C/Cython
+
+* Improve finding of modes with zero velocity or infinite decay length
+  Right now a mode with truly zero velocity may be incorrectly identified as
+  propagating or evanescent.