diff --git a/unsloth/models/loader.py b/unsloth/models/loader.py
index bc98c0dc19..efbf4ed37c 100644
--- a/unsloth/models/loader.py
+++ b/unsloth/models/loader.py
@@ -592,7 +592,7 @@ class FastModel(FastBaseModel):
                 "os.environ['TRITON_F32_DEFAULT'] = 'ieee';"
         elif "gpt-oss" in lowered_model_name:
             os.environ["UNSLOTH_DISABLE_STATIC_GENERATION"] = "1"
-            if not model_name:
+            if not load_in_4bit:
                 # Only upcast MoE biases for MXFP4, not BnB
                 os.environ["UNSLOTH_FORCE_CUSTOM_DTYPE"] = \
                     "all;None;None;"\