diff --git a/tensorflow_probability/python/experimental/mcmc/particle_filter.py b/tensorflow_probability/python/experimental/mcmc/particle_filter.py
index 134c35514d..2322d5a5ec 100644
--- a/tensorflow_probability/python/experimental/mcmc/particle_filter.py
+++ b/tensorflow_probability/python/experimental/mcmc/particle_filter.py
@@ -605,9 +605,8 @@ def _outer_particle_filter_propose_and_update_log_weights_fn(
 ):
   """Build a function specifying a particle filter update step."""
   def _outer_propose_and_update_log_weights_fn(step, state, seed=None):
-    outside_parameters = state.particles[0]
     (
-        params,
+        outside_parameters,
         inner_particles,
         inner_parent_indices,
         inner_incremental_likelihood,