diff --git a/tensorflow_probability/python/experimental/mcmc/particle_filter.py b/tensorflow_probability/python/experimental/mcmc/particle_filter.py
index 9c83fbbbe4..34ac008615 100644
--- a/tensorflow_probability/python/experimental/mcmc/particle_filter.py
+++ b/tensorflow_probability/python/experimental/mcmc/particle_filter.py
@@ -1105,9 +1105,9 @@ def _compute_observation_log_weights(step,
     observation = tf.nest.map_structure(
         lambda x, step=step: tf.gather(x, observation_idx), observations)
     if particles_dim != 0:
-        observation = tf.nest.map_structure(
-            lambda x: tf.expand_dims(x, axis=particles_dim), observation
-        )
+      observation = tf.nest.map_structure(
+          lambda x: tf.expand_dims(x, axis=particles_dim), observation
+      )
 
     log_weights = observation_fn(step, particles).log_prob(observation)
     return tf.where(step_has_observation,