diff --git a/compiler/rustc_mir_transform/src/deduce_param_attrs.rs b/compiler/rustc_mir_transform/src/deduce_param_attrs.rs
index 79645310a3987..990cfb05e607e 100644
--- a/compiler/rustc_mir_transform/src/deduce_param_attrs.rs
+++ b/compiler/rustc_mir_transform/src/deduce_param_attrs.rs
@@ -44,6 +44,7 @@ impl<'tcx> Visitor<'tcx> for DeduceReadOnly {
                 // Whether mutating though a `&raw const` is allowed is still undecided, so we
                 // disable any sketchy `readonly` optimizations for now.
                 // But we only need to do this if the pointer would point into the argument.
+                // IOW: for indirect places, like `&raw (*local).field`, this surely cannot mutate `local`.
                 !place.is_indirect()
             }
             PlaceContext::NonMutatingUse(..) | PlaceContext::NonUse(..) => {