diff --git a/src/datasets/arrow_dataset.py b/src/datasets/arrow_dataset.py
index 1d450891a72..f577ea298d7 100644
--- a/src/datasets/arrow_dataset.py
+++ b/src/datasets/arrow_dataset.py
@@ -4051,7 +4051,7 @@ def sort(
             )
 
         # Check proper format of and for duplicates in column_names
-        if not isinstance(column_names, list):
+        if isinstance(column_names, str):
             column_names = [column_names]
 
         # Check proper format and length of reverse