diff --git a/src/test/mir-opt/issue-43457.rs b/src/test/mir-opt/issue-43457.rs
new file mode 100644
index 0000000000000..708784df317a6
--- /dev/null
+++ b/src/test/mir-opt/issue-43457.rs
@@ -0,0 +1,55 @@
+// Copyright 2017 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+// compile-flags: -Z identify_regions -Z span_free_formats
+// ignore-tidy-linelength
+
+// Regression test for #43457: an `EndRegion` was missing from output
+// because compiler was using a faulty means for region map lookup.
+
+use std::cell::RefCell;
+
+fn rc_refcell_test(r: RefCell<i32>) {
+    r.borrow_mut();
+}
+
+fn main() { }
+
+// END RUST SOURCE
+// START rustc.node5.SimplifyCfg-qualify-consts.after.mir
+//
+// fn rc_refcell_test(_1: std::cell::RefCell<i32>) -> () {
+//     let mut _0: ();
+//     scope 1 {
+//         let _2: std::cell::RefCell<i32>;
+//     }
+//     let mut _3: std::cell::RefMut<'17dce, i32>;
+//     let mut _4: &'17dce std::cell::RefCell<i32>;
+//
+//     bb0: {
+//         StorageLive(_2);
+//         _2 = _1;
+//         StorageLive(_4);
+//         _4 = &'17dce _2;
+//         _3 = const <std::cell::RefCell<T>>::borrow_mut(_4) -> bb1;
+//     }
+//
+//     bb1: {
+//         drop(_3) -> bb2;
+//     }
+//
+//     bb2: {
+//         StorageDead(_4);
+//         EndRegion('17dce);
+//         _0 = ();
+//         StorageDead(_2);
+//         return;
+//     }
+// }