1 files changed, 18 insertions, 0 deletions

diff --git a/tests/ui/issues/issue-20544.rs b/tests/ui/issues/issue-20544.rs
new file mode 100644
index 00000000000..0f4d314f166
--- /dev/null
+++ b/tests/ui/issues/issue-20544.rs
@@ -0,0 +1,18 @@
+// run-pass
+#![feature(unboxed_closures)]
+#![feature(fn_traits)]
+
+struct Fun<F>(F);
+
+impl<F, T> FnOnce<(T,)> for Fun<F> where F: Fn(T) -> T {
+    type Output = T;
+
+    extern "rust-call" fn call_once(self, (t,): (T,)) -> T {
+        (self.0)(t)
+    }
+}
+
+fn main() {
+    let fun = Fun(|i: isize| i * 2);
+    println!("{}", fun(3));
+}