diff --git a/compiler/rustc_infer/src/infer/region_constraints/leak_check.rs b/compiler/rustc_infer/src/infer/region_constraints/leak_check.rs
index 36d18aebfe2..817aaf10053 100644
--- a/compiler/rustc_infer/src/infer/region_constraints/leak_check.rs
+++ b/compiler/rustc_infer/src/infer/region_constraints/leak_check.rs
@@ -100,6 +100,7 @@ pub fn leak_check(
 struct LeakCheck<'me, 'tcx> {
     tcx: TyCtxt<'tcx>,
     universe_at_start_of_snapshot: ty::UniverseIndex,
+    /// Only used when reporting region errors.
     overly_polymorphic: bool,
     mini_graph: &'me MiniGraph<'tcx>,
     rcc: &'me RegionConstraintCollector<'me, 'tcx>,