diff --git a/pyro/poutine/indep_messenger.py b/pyro/poutine/indep_messenger.py
index 3d68136b9a..c224b032fd 100644
--- a/pyro/poutine/indep_messenger.py
+++ b/pyro/poutine/indep_messenger.py
@@ -2,7 +2,8 @@
 # SPDX-License-Identifier: Apache-2.0
 
 import numbers
-from typing import Iterator, NamedTuple, Optional, Tuple
+from dataclasses import dataclass
+from typing import Iterator, Optional, Tuple
 
 import torch
 from typing_extensions import Self
@@ -12,7 +13,8 @@
 from pyro.util import ignore_jit_warnings
 
 
-class CondIndepStackFrame(NamedTuple):
+@dataclass
+class CondIndepStackFrame:
     name: str
     dim: Optional[int]
     size: int
@@ -97,7 +99,6 @@ def __enter__(self) -> Self:
             self._vectorized = True
 
         if self._vectorized is True:
-            assert self.dim is not None
             self.dim = _DIM_ALLOCATOR.allocate(self.name, self.dim)
 
         return super().__enter__()