diff --git a/compiler/rustc_smir/src/rustc_internal/mod.rs b/compiler/rustc_smir/src/rustc_internal/mod.rs
index 4d2a518226d..f0b368bec39 100644
--- a/compiler/rustc_smir/src/rustc_internal/mod.rs
+++ b/compiler/rustc_smir/src/rustc_internal/mod.rs
@@ -104,6 +104,10 @@ impl<'tcx> Tables<'tcx> {
         stable_mir::ty::RegionDef(self.create_def_id(did))
     }
 
+    pub fn coroutine_witness_def(&mut self, did: DefId) -> stable_mir::ty::CoroutineWitnessDef {
+        stable_mir::ty::CoroutineWitnessDef(self.create_def_id(did))
+    }
+
     pub fn prov(&mut self, aid: AllocId) -> stable_mir::ty::Prov {
         stable_mir::ty::Prov(self.create_alloc_id(aid))
     }
diff --git a/compiler/rustc_smir/src/rustc_smir/mod.rs b/compiler/rustc_smir/src/rustc_smir/mod.rs
index d3bd87bb360..170f53a7a69 100644
--- a/compiler/rustc_smir/src/rustc_smir/mod.rs
+++ b/compiler/rustc_smir/src/rustc_smir/mod.rs
@@ -1292,7 +1292,11 @@ impl<'tcx> Stable<'tcx> for ty::TyKind<'tcx> {
             ty::Bound(debruijn_idx, bound_ty) => {
                 TyKind::Bound(debruijn_idx.as_usize(), bound_ty.stable(tables))
             }
-            ty::Placeholder(..) | ty::CoroutineWitness(..) | ty::Infer(_) | ty::Error(_) => {
+            ty::CoroutineWitness(def_id, args) => TyKind::RigidTy(RigidTy::CoroutineWitness(
+                tables.coroutine_witness_def(*def_id),
+                args.stable(tables),
+            )),
+            ty::Placeholder(..) | ty::Infer(_) | ty::Error(_) => {
                 unreachable!();
             }
         }
diff --git a/compiler/stable_mir/src/ty.rs b/compiler/stable_mir/src/ty.rs
index bd3feef6018..d2f1f3af0ce 100644
--- a/compiler/stable_mir/src/ty.rs
+++ b/compiler/stable_mir/src/ty.rs
@@ -156,6 +156,7 @@ pub enum RigidTy {
     Dynamic(Vec<Binder<ExistentialPredicate>>, Region, DynKind),
     Never,
     Tuple(Vec<Ty>),
+    CoroutineWitness(CoroutineWitnessDef, GenericArgs),
 }
 
 #[derive(Clone, Copy, Debug, PartialEq, Eq)]
@@ -235,6 +236,9 @@ pub struct ImplDef(pub DefId);
 #[derive(Clone, PartialEq, Eq, Debug)]
 pub struct RegionDef(pub DefId);
 
+#[derive(Clone, PartialEq, Eq, Debug)]
+pub struct CoroutineWitnessDef(pub DefId);
+
 /// A list of generic arguments.
 #[derive(Clone, Debug, Eq, PartialEq)]
 pub struct GenericArgs(pub Vec<GenericArgKind>);
diff --git a/compiler/stable_mir/src/visitor.rs b/compiler/stable_mir/src/visitor.rs
index 05e0b9b4d78..65e42879d61 100644
--- a/compiler/stable_mir/src/visitor.rs
+++ b/compiler/stable_mir/src/visitor.rs
@@ -149,6 +149,7 @@ impl Visitable for RigidTy {
             RigidTy::FnPtr(sig) => sig.visit(visitor),
             RigidTy::Closure(_, args) => args.visit(visitor),
             RigidTy::Coroutine(_, args, _) => args.visit(visitor),
+            RigidTy::CoroutineWitness(_, args) => args.visit(visitor),
             RigidTy::Dynamic(pred, r, _) => {
                 pred.visit(visitor)?;
                 r.visit(visitor)