diff --git a/src/_bentoml_sdk/io_models.py b/src/_bentoml_sdk/io_models.py
index 70201e59d7a..e8cac360625 100644
--- a/src/_bentoml_sdk/io_models.py
+++ b/src/_bentoml_sdk/io_models.py
@@ -81,7 +81,7 @@ def mime_type(cls) -> str:
                 return "audio/*"
             elif format == "video":
                 return "video/*"
-            return "*/*"
+            return "application/octet-stream"
         return "application/json"
 
     @classmethod
@@ -178,9 +178,7 @@ def content_stream() -> t.Generator[str | bytes, None, None]:
         else:
             if is_file_type(type(obj)) and isinstance(serde, JSONSerde):
                 if isinstance(obj, pathlib.PurePath):
-                    media_type = (
-                        mimetypes.guess_type(obj)[0] or "application/octet-stream"
-                    )
+                    media_type = mimetypes.guess_type(obj)[0] or cls.mime_type()
                     should_inline = media_type.startswith("image")
                     content_disposition_type = (
                         "inline" if should_inline else "attachment"
@@ -310,7 +308,9 @@ def from_output(cls, func: t.Callable[..., t.Any]) -> type[IODescriptor]:
 
 
 def ensure_io_descriptor(output_type: type) -> type[IODescriptor]:
-    if inspect.isclass(output_type) and issubclass(output_type, BaseModel):
+    from pydantic._internal._utils import lenient_issubclass
+
+    if inspect.isclass(output_type) and lenient_issubclass(output_type, BaseModel):
         if not issubclass(output_type, IODescriptor):
             return t.cast(
                 t.Type[IODescriptor],