diff --git a/src/librustc_mir/borrow_check/nll/type_check/mod.rs b/src/librustc_mir/borrow_check/nll/type_check/mod.rs
index eafb12fab964..d57b8e78f18a 100644
--- a/src/librustc_mir/borrow_check/nll/type_check/mod.rs
+++ b/src/librustc_mir/borrow_check/nll/type_check/mod.rs
@@ -1585,6 +1585,8 @@ impl MirPass for TypeckMir {
         let id = tcx.hir.as_local_node_id(def_id).unwrap();
         debug!("run_pass: {:?}", def_id);
 
+        // When NLL is enabled, the borrow checker runs the typeck
+        // itself, so we don't need this MIR pass anymore.
         if tcx.sess.nll() {
             return;
         }