diff --git a/requirements.txt b/requirements.txt
index 0bd0a93..24c413c 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -3,4 +3,4 @@ progressbar2~=3.53.1
 tokenizers>=0.10.3
 transformers>=4.6.1
 sudachipy>=0.6.2
-sudachidict_core>=20210802
+sudachidict_core==20210802.*
\ No newline at end of file
diff --git a/sudachitra/tokenization_bert_sudachipy.py b/sudachitra/tokenization_bert_sudachipy.py
index 8173543..fccb0b8 100644
--- a/sudachitra/tokenization_bert_sudachipy.py
+++ b/sudachitra/tokenization_bert_sudachipy.py
@@ -152,22 +152,6 @@ def __init__(
             sudachipy_kwargs=None,
             **kwargs
     ):
-        super().__init__(
-            do_lower_case=do_lower_case,
-            do_nfkc=do_nfkc,
-            do_word_tokenize=do_word_tokenize,
-            do_subword_tokenize=do_subword_tokenize,
-            word_tokenizer_type=word_tokenizer_type,
-            subword_tokenizer_type=subword_tokenizer_type,
-            unk_token=unk_token,
-            sep_token=sep_token,
-            pad_token=pad_token,
-            cls_token=cls_token,
-            mask_token=mask_token,
-            word_form_type=word_form_type,
-            sudachipy_kwargs=sudachipy_kwargs,
-            **kwargs,
-        )
 
         if not os.path.isfile(vocab_file):
             raise ValueError(f"Can't find a vocabulary file at path '{vocab_file}'.")
@@ -196,12 +180,30 @@ def __init__(
             if subword_tokenizer_type == "pos_substitution":
                 self.subword_tokenizer = None
             elif subword_tokenizer_type == "wordpiece":
-                self.subword_tokenizer = WordpieceTokenizer(vocab=self.vocab, unk_token=self.unk_token)
+                self.subword_tokenizer = WordpieceTokenizer(vocab=self.vocab, unk_token=str(unk_token))
             elif subword_tokenizer_type == "character":
-                self.subword_tokenizer = CharacterTokenizer(vocab=self.vocab, unk_token=self.unk_token)
+                self.subword_tokenizer = CharacterTokenizer(vocab=self.vocab, unk_token=str(unk_token))
             else:
                 raise ValueError(f"Invalid subword_tokenizer_type '{subword_tokenizer_type}' is specified.")
 
+        super().__init__(
+            do_lower_case=do_lower_case,
+            do_nfkc=do_nfkc,
+            do_word_tokenize=do_word_tokenize,
+            do_subword_tokenize=do_subword_tokenize,
+            word_tokenizer_type=word_tokenizer_type,
+            subword_tokenizer_type=subword_tokenizer_type,
+            unk_token=unk_token,
+            sep_token=sep_token,
+            pad_token=pad_token,
+            cls_token=cls_token,
+            mask_token=mask_token,
+            word_form_type=word_form_type,
+            sudachipy_kwargs=sudachipy_kwargs,
+            **kwargs,
+        )
+
+
     @property
     def do_lower_case(self):
         return self.lower_case