diff --git a/modelopt/torch/export/plugins/mcore_custom.py b/modelopt/torch/export/plugins/mcore_custom.py
index 204ff012c71..fd06e9f384c 100644
--- a/modelopt/torch/export/plugins/mcore_custom.py
+++ b/modelopt/torch/export/plugins/mcore_custom.py
@@ -305,6 +305,12 @@ def save_safetensors_by_layer_index(
         meta_filename = filename + ".json"
         ckpt_filename = filename + ".safetensors"
 
+        # Write safetensors first, then build the per-layer meta JSON from the same dict.
+        # Order matters: any late mutations to layer_state_dict (e.g. MTP tensors added after
+        # the dict was first constructed) must be captured by both files.  Writing safetensors
+        # first ensures the JSON is always consistent with what is physically on disk.
+        save_file(layer_state_dict, save_directory + "/" + ckpt_filename, metadata={"format": "pt"})
+
         weight_map = {}
         layer_total_size = 0
         for key, val in layer_state_dict.items():
@@ -318,7 +324,6 @@ def save_safetensors_by_layer_index(
                 f,
                 indent=4,
             )
-        save_file(layer_state_dict, save_directory + "/" + ckpt_filename, metadata={"format": "pt"})
 
     # [TODO]: this global barrier needs to be replaced with something safer
     torch.distributed.barrier()