diff --git a/torchtune/training/checkpointing/_checkpointer.py b/torchtune/training/checkpointing/_checkpointer.py
index 48aa57e84..559fca84b 100644
--- a/torchtune/training/checkpointing/_checkpointer.py
+++ b/torchtune/training/checkpointing/_checkpointer.py
@@ -743,10 +743,8 @@ def save_checkpoint(
                 index_file_name = TORCH_INDEX_FNAME
 
             index_path = Path.joinpath(
-                self._output_dir,
-                f"epoch_{epoch}",
-                index_file_name,
-            ).with_suffix(".json")
+                self._output_dir, f"epoch_{epoch}", index_file_name
+            )
 
             index_data = {
                 "metadata": {"total_size": total_size},
diff --git a/torchtune/training/checkpointing/_utils.py b/torchtune/training/checkpointing/_utils.py
index 82f60fc7d..770a3f889 100644
--- a/torchtune/training/checkpointing/_utils.py
+++ b/torchtune/training/checkpointing/_utils.py
@@ -32,8 +32,8 @@
 # https://github.com/huggingface/peft/blob/d13d7a401ccf4808aaaf76480fea09a4cf4ac1f5/src/peft/config.py#L259C21-L259C32
 ADAPTER_CONFIG_FNAME = "adapter_config"
 ADAPTER_MODEL_FNAME = "adapter_model"
-SAFETENSOR_INDEX_FNAME = "model.safetensors.index"
-TORCH_INDEX_FNAME = "pytorch_model.bin.index"
+SAFETENSOR_INDEX_FNAME = "model.safetensors.index.json"
+TORCH_INDEX_FNAME = "pytorch_model.bin.index.json"
 
 # standardize checkpointing
 SHARD_FNAME = "ft-model-{cpt_idx}-of-{num_shards}"