diff --git a/gcc/testsuite/rust/compile/issue-3599.rs b/gcc/testsuite/rust/compile/issue-3599.rs
new file mode 100644
index 000000000000..1d29fac84e93
--- /dev/null
+++ b/gcc/testsuite/rust/compile/issue-3599.rs
@@ -0,0 +1,8 @@
+#[lang = "sized"]
+trait Sized {}
+
+trait Bar {}
+
+struct S; // { dg-warning "struct is never constructed" }
+
+pub fn test(foo: impl Bar) {}