diff --git a/rag/flow/tokenizer/tokenizer.py b/rag/flow/tokenizer/tokenizer.py
index 6b7d6ad2a..686a0bb7e 100644
--- a/rag/flow/tokenizer/tokenizer.py
+++ b/rag/flow/tokenizer/tokenizer.py
@@ -63,6 +63,8 @@ class Tokenizer(ProcessBase):
         texts = []
         for c in chunks:
             txt = ""
+            if isinstance(self._param.fields, str):
+                self._param.fields=[self._param.fields]
             for f in self._param.fields:
                 f = c.get(f)
                 if isinstance(f, str):