diff --git a/doc/rust.md b/doc/rust.md
index 3a3c371accdfd6a6fdbe1268a233f0ebc202ac5d..210e07d198acc8006a09b4a8190f056d1495b9e9 100644
--- a/doc/rust.md
+++ b/doc/rust.md
@@ -876,6 +876,13 @@ fn add(x: int, y: int) -> int {
 }
 ~~~~
 
+As with `let` bindings, function arguments are irrefutable patterns,
+so any pattern that is valid in a let binding is also valid as an argument.
+
+~~~
+fn first((value, _): (int, int)) -> int { value }
+~~~
+
 
 #### Generic functions