diff --git a/gguf-py/gguf/gguf_reader.py b/gguf-py/gguf/gguf_reader.py
index 5991cdb76beac..d87e8f72321b3 100644
--- a/gguf-py/gguf/gguf_reader.py
+++ b/gguf-py/gguf/gguf_reader.py
@@ -251,7 +251,7 @@ def _get_field_parts(
                 offs += curr_size
             return offs - orig_offs, aparts, data_idxs, types
         # We can't deal with this one.
-        raise ValueError('Unknown/unhandled field type {gtype}')
+        raise ValueError(f'Unknown/unhandled field type {gtype}')
 
     def _get_tensor_info_field(self, orig_offs: int) -> ReaderField:
         offs = orig_offs