diff --git a/src/openai/_files.py b/src/openai/_files.py
index 7b23ca084a..b91060e51c 100644
--- a/src/openai/_files.py
+++ b/src/openai/_files.py
@@ -97,7 +97,7 @@ async def async_to_httpx_files(files: RequestFiles | None) -> HttpxRequestFiles
     elif is_sequence_t(files):
         files = [(key, await _async_transform_file(file)) for key, file in files]
     else:
-        raise TypeError("Unexpected file type input {type(files)}, expected mapping or sequence")
+        raise TypeError(f"Unexpected file type input {type(files)}, expected mapping or sequence")
 
     return files