diff --git a/tests/ui/str/debug-print-basic-tuple.rs b/tests/ui/str/debug-print-basic-tuple.rs
index 89beaa222273..7e2b86f56293 100644
--- a/tests/ui/str/debug-print-basic-tuple.rs
+++ b/tests/ui/str/debug-print-basic-tuple.rs
@@ -1,3 +1,4 @@
+//! regression test for <https://github.com/rust-lang/rust/issues/3109>
 //@ run-pass
 pub fn main() {
     println!("{:?}", ("hi there!", "you"));