diff --git a/tests/test_sft_trainer.py b/tests/test_sft_trainer.py
index e615caf0431..02ef4d1b039 100644
--- a/tests/test_sft_trainer.py
+++ b/tests/test_sft_trainer.py
@@ -39,6 +39,10 @@ def formatting_prompts_func(example):
     return text
 
 
+def formatting_func_for_pretokenized(example):
+    return example["input_ids"]
+
+
 def formatting_prompts_func_batched(example):
     output_text = []
     for i, question in enumerate(example["question"]):
@@ -93,6 +97,17 @@ def setUp(self):
                 ],
             }
         )
+        self.dummy_tokenized_dataset = Dataset.from_dict(
+            {
+                "input_ids": [
+                    self.tokenizer.encode(
+                        "TRL is a library to post-train LLMs and diffusion models with methods such as Supervised Fine-tuning (SFT), Proximal Policy Optimization (PPO), and Direct Preference Optimization (DPO)."
+                    )
+                ]
+                * 10
+            }
+        )
+
         self.conversational_lm_dataset = load_dataset("trl-internal-testing/zen", "conversational_language_modeling")
         self.standard_prompt_completion_dataset = load_dataset(
             "trl-internal-testing/zen", "standard_prompt_completion"
@@ -105,7 +120,10 @@ def setUp(self):
                         [
                             {
                                 "role": "user",
-                                "content": [{"type": "text", "text": "What is in this image?"}, {"type": "image"}],
+                                "content": [
+                                    {"type": "text", "text": "What is in this image?"},
+                                    {"type": "image"},
+                                ],
                             },
                             {
                                 "role": "assistant",
@@ -113,7 +131,12 @@ def setUp(self):
                             },
                             {
                                 "role": "user",
-                                "content": [{"type": "text", "text": "Oh ye, you are right, what is 1+1"}],
+                                "content": [
+                                    {
+                                        "type": "text",
+                                        "text": "Oh ye, you are right, what is 1+1",
+                                    }
+                                ],
                             },
                             {
                                 "role": "assistant",
@@ -123,7 +146,10 @@ def setUp(self):
                         [
                             {
                                 "role": "user",
-                                "content": [{"type": "text", "text": "What is in this image?"}, {"type": "image"}],
+                                "content": [
+                                    {"type": "text", "text": "What is in this image?"},
+                                    {"type": "image"},
+                                ],
                             },
                             {
                                 "role": "assistant",
@@ -158,6 +184,45 @@ def setUp(self):
             num_of_sequences=16,
         )
 
+        self.train_dataset_from_pretokenized = ConstantLengthDataset(
+            self.tokenizer,
+            self.dummy_tokenized_dataset,
+            dataset_text_field=None,
+            seq_length=16,
+            num_of_sequences=16,
+            formatting_func=formatting_func_for_pretokenized,
+        )
+
+        self.eval_dataset_from_pretokenized = ConstantLengthDataset(
+            self.tokenizer,
+            self.dummy_tokenized_dataset,
+            dataset_text_field=None,
+            seq_length=16,
+            num_of_sequences=16,
+            formatting_func=formatting_func_for_pretokenized,
+        )
+
+    def test_constant_length_dataset_with_pretokenized_data(self):
+        constant_len_dataset = ConstantLengthDataset(
+            self.tokenizer,
+            self.dummy_tokenized_dataset,
+            dataset_text_field=None,
+            formatting_func=formatting_func_for_pretokenized,
+        )
+
+        assert len(constant_len_dataset) == len(self.dummy_tokenized_dataset)
+        assert len(constant_len_dataset) > 0
+
+        for example in constant_len_dataset:
+            assert "input_ids" in example
+            assert "labels" in example
+
+            assert len(example["input_ids"]) == constant_len_dataset.seq_length
+            assert len(example["labels"]) == constant_len_dataset.seq_length
+
+            decoded_text = self.tokenizer.decode(example["input_ids"])
+            assert ("TRL" in decoded_text) and ("(DPO)" in decoded_text)
+
     def test_constant_length_dataset(self):
         formatted_dataset = ConstantLengthDataset(
             self.tokenizer,
@@ -236,6 +301,34 @@ def test_sft_trainer(self):
 
             self.assertIn("model.safetensors", os.listdir(tmp_dir + "/checkpoint-2"))
 
+    def test_sft_trainer_with_pretokenzied_data_packing(self):
+        with tempfile.TemporaryDirectory() as tmp_dir:
+            training_args = SFTConfig(
+                output_dir=tmp_dir,
+                dataloader_drop_last=True,
+                eval_strategy="steps",
+                max_steps=4,
+                eval_steps=2,
+                save_steps=2,
+                per_device_train_batch_size=2,
+                packing=True,
+                report_to="none",
+            )
+
+            trainer = SFTTrainer(
+                model=self.model_id,
+                args=training_args,
+                train_dataset=self.train_dataset_from_pretokenized,
+                eval_dataset=self.eval_dataset_from_pretokenized,
+            )
+
+            trainer.train()
+
+            assert trainer.state.log_history[(-1)]["train_loss"] is not None
+            assert trainer.state.log_history[0]["eval_loss"] is not None
+
+            assert "model.safetensors" in os.listdir(tmp_dir + "/checkpoint-2")
+
     def test_sft_trainer_uncorrect_data(self):
         with tempfile.TemporaryDirectory() as tmp_dir:
             # Shoud work as SFTTrainer natively supports conversational lm dataset
diff --git a/trl/trainer/utils.py b/trl/trainer/utils.py
index c9ea619d63f..f2854a1cec0 100644
--- a/trl/trainer/utils.py
+++ b/trl/trainer/utils.py
@@ -622,8 +622,8 @@ def __init__(
         else:  # neither is provided
             raise ValueError("Either `dataset_text_field` or `formatting_func` should be provided.")
 
-        if self.formatting_func is not None:
-            if self.formatting_func.__code__.co_argcount > 1:
+        if formatting_func is not None:
+            if formatting_func.__code__.co_argcount > 1:
                 warnings.warn(
                     "The passed formatting_func has more than one argument. Usually that function should have a single argument `example`"
                     " which corresponds to the dictionary returned by each element of the dataset. Make sure you know what you are doing."