diff --git a/src/transformers/tokenization_utils_fast.py b/src/transformers/tokenization_utils_fast.py
index 724484b3b30b..94815caf352c 100644
--- a/src/transformers/tokenization_utils_fast.py
+++ b/src/transformers/tokenization_utils_fast.py
@@ -824,7 +824,16 @@ def train_new_from_iterator(
             kwargs["end_of_word_suffix"] = tokenizer_json["model"]["end_of_word_suffix"]
         if tokenizer_json["model"]["type"] == "Unigram" and unk_token is not None:
             kwargs["unk_token"] = unk_token
-        if tokenizer_json["pre_tokenizer"] is not None and tokenizer_json["pre_tokenizer"]["type"] == "ByteLevel":
+        if (
+            tokenizer_json["pre_tokenizer"] is not None
+            and tokenizer_json["pre_tokenizer"]["type"] == "ByteLevel"
+            or tokenizer_json["pre_tokenizer"]["type"] == "Sequence"
+            and "pretokenizers" in tokenizer_json["pre_tokenizer"]
+            and any(
+                pretokenizer["type"] == "ByteLevel"
+                for pretokenizer in tokenizer_json["pre_tokenizer"]["pretokenizers"]
+            )
+        ):
             kwargs["initial_alphabet"] = pre_tokenizers_fast.ByteLevel.alphabet()
 
         trainer_class = MODEL_TO_TRAINER_MAPPING[tokenizer_json["model"]["type"]]