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</replaceable> lies beyond the end of the string, only the
     substring up to the end of the string is returned.
     <replaceable>start</replaceable> must be
-    non-negative.</para></listitem>
+    non-negative. For example,
+
+<programlisting>
+builtins.substring 0 3 "nixos"
+</programlisting>
+
+   evaluates to <literal>"nix"</literal>.
+   </para></listitem>
 
   </varlistentry>