diff --git a/source/numerics.tex b/source/numerics.tex
index 9fedf97488..b072589f4c 100644
--- a/source/numerics.tex
+++ b/source/numerics.tex
@@ -18923,7 +18923,7 @@
 \begin{itemize}
 \item
 \exposid{set-indices} be a list of the index positions of \tcode{true}
-elements in \tcode{selector}.
+elements in \tcode{selector}, in ascending order.
 \item
 \tcode{\exposidnc{bit-lookup}($b$)} be a function which returns the index
 where $b$ appears in \tcode{\exposid{set-indices}}.