diff --git a/vllm/config.py b/vllm/config.py
index 84746bd41c205..29deec03638e0 100644
--- a/vllm/config.py
+++ b/vllm/config.py
@@ -164,7 +164,9 @@ def _verify_load_format(self) -> None:
 
         # TODO: Remove this check once HF updates the pt weights of Mixtral.
         architectures = getattr(self.hf_config, "architectures", [])
-        if "MixtralForCausalLM" in architectures and load_format == "pt":
+        # architectures can be None instead of []
+        if architectures and "MixtralForCausalLM" in architectures \
+            and load_format == "pt":
             raise ValueError(
                 "Currently, the 'pt' format is not supported for Mixtral. "
                 "Please use the 'safetensors' format instead. ")