diff --git a/taxoniumtools/src/taxoniumtools/utils.py b/taxoniumtools/src/taxoniumtools/utils.py
index 0a92c75d..344e28a4 100644
--- a/taxoniumtools/src/taxoniumtools/utils.py
+++ b/taxoniumtools/src/taxoniumtools/utils.py
@@ -28,7 +28,9 @@ def read_metadata(metadata_file, columns, key_column):
         metadata.set_index(key_column, inplace=True)
         # convert metadata to dict of rows
         if not metadata.index.is_unique:
-            print(f"Error: The key column '{key_column}' contains non-unique values in the metadata file.")
+            print(
+                f"Error: The key column '{key_column}' contains non-unique values in the metadata file."
+            )
 
         metadata_dict = metadata.to_dict("index")
         metadata_cols = metadata.columns