diff --git a/torchy_baselines/ppo/ppo.py b/torchy_baselines/ppo/ppo.py
index e9d8bdf..d9496f0 100644
--- a/torchy_baselines/ppo/ppo.py
+++ b/torchy_baselines/ppo/ppo.py
@@ -135,6 +135,10 @@ class PPO(BaseRLModel):
 
         self.clip_range = get_schedule_fn(self.clip_range)
         if self.clip_range_vf is not None:
+            if isinstance(self.clip_range_vf, (float, int)):
+                assert self.clip_range_vf > 0, ('`clip_range_vf` must be positive, '
+                                                'pass `None` to deactivate vf clipping')
+
             self.clip_range_vf = get_schedule_fn(self.clip_range_vf)
 
     def collect_rollouts(self,