diff --git a/modelopt/torch/export/unified_export_megatron.py b/modelopt/torch/export/unified_export_megatron.py
index f1bd67327..625e62f97 100644
--- a/modelopt/torch/export/unified_export_megatron.py
+++ b/modelopt/torch/export/unified_export_megatron.py
@@ -331,6 +331,9 @@ def save_pretrained(
                     "exclude_modules": ["lm_head"],
                 },
             }
+            if "NVFP4" in quantization:
+                # for vllm, the group size is required
+                hf_quant_config["quantization"]["group_size"] = 16
             with open(save_directory + "/hf_quant_config.json", "w") as f:
                 json.dump(hf_quant_config, f, indent=4)