diff --git a/doc/manual/expressions/builtins.xml b/doc/manual/expressions/builtins.xml
index 5fd93c831..6ac802343 100644
--- a/doc/manual/expressions/builtins.xml
+++ b/doc/manual/expressions/builtins.xml
@@ -853,7 +853,14 @@ builtins.sort builtins.lessThan [ 483 249 526 147 42 77 ]
len lies beyond the end of the string, only the
substring up to the end of the string is returned.
start must be
- non-negative.
+ non-negative. For example,
+
+
+builtins.substring 0 3 "nixos"
+
+
+ evaluates to "nix".
+