diff --git a/compiler/rustc_middle/src/thir.rs b/compiler/rustc_middle/src/thir.rs
index 7ffa88afa159..ee11a75529b8 100644
--- a/compiler/rustc_middle/src/thir.rs
+++ b/compiler/rustc_middle/src/thir.rs
@@ -815,7 +815,9 @@ pub enum PatKind<'tcx> {
 /// The boundaries must be of the same type and that type must be numeric.
 #[derive(Clone, Debug, PartialEq, HashStable, TypeVisitable)]
 pub struct PatRange<'tcx> {
+    /// Must not be `PosInfinity`.
     pub lo: PatRangeBoundary<'tcx>,
+    /// Must not be `NegInfinity`.
     pub hi: PatRangeBoundary<'tcx>,
     #[type_visitable(ignore)]
     pub end: RangeEnd,