diff --git a/metastable_baselines/ppo/policies.py b/metastable_baselines/ppo/policies.py
index 644c56a..2cd7e08 100644
--- a/metastable_baselines/ppo/policies.py
+++ b/metastable_baselines/ppo/policies.py
@@ -299,7 +299,7 @@ class ActorCriticPolicy(BasePolicy):
         values = self.value_net(latent_vf)
         distribution = self._get_action_dist_from_latent(latent_pi)
         if self.use_pca:
-            assert trajectory, 'Past trajetcory has to be provided when using PCA.'
+            assert trajectory != None, 'Past trajectory has to be provided when using PCA.'
             actions = distribution.get_actions(deterministic=deterministic, trajectory=trajectory)
         else:
             actions = distribution.get_actions(deterministic=deterministic)