diff --git a/trl/trainer/ppo_trainer.py b/trl/trainer/ppo_trainer.py
index 51897eeb44..804f2b427b 100644
--- a/trl/trainer/ppo_trainer.py
+++ b/trl/trainer/ppo_trainer.py
@@ -138,10 +138,19 @@ def __init__(
         if data_collator is None:
             data_collator = DataCollatorWithPadding(self.processing_class)
 
-        self.policy_model.generation_config.eos_token_id = (
-            None  # disable `pad_token_id` and `eos_token_id` because we just want to
-        )
-        self.policy_model.generation_config.pad_token_id = None  # generate tokens without truncation / padding
+        # Handle stop token settings
+        if args.stop_token and args.stop_token_id:
+            raise ValueError("You cannot set both `stop_token` and `stop_token_id`. ")
+        if args.stop_token:
+            if args.stop_token == "eos":
+                args.stop_token_id = processing_class.eos_token_id
+            else:
+                raise ValueError(
+                    f"Unknown `stop_token` {args.stop_token}. "
+                    f"Allowed values are: `eos`, None (no stop token)"
+                )
+        # Update policy model's generation_config to use provided stop token
+        self.policy_model.generation_config.eos_token_id = args.stop_token_id
 
         # peft support
         if not is_peft_available() and peft_config is not None:
@@ -220,8 +229,6 @@ def __init__(
         for module in [self.policy_model, self.ref_model, self.value_model, self.reward_model]:
             if module is not None:
                 disable_dropout_in_model(module)
-        if args.stop_token and args.stop_token == "eos":
-            args.stop_token_id = processing_class.eos_token_id
         self.model = PolicyAndValueWrapper(self.policy_model, self.value_model)
         self.model.config = self.policy_model.config  # needed for pushing to hub
         self.create_optimizer_and_scheduler(