diff --git a/litgpt/tokenizer.py b/litgpt/tokenizer.py
index 2a3028de58..cace23dfbd 100644
--- a/litgpt/tokenizer.py
+++ b/litgpt/tokenizer.py
@@ -73,7 +73,7 @@ def __init__(self, checkpoint_dir: Path | str) -> None:
         self.apply_decoding_fix = None
         if (config_path := checkpoint_dir / "tokenizer_config.json").is_file():
             with open(config_path, encoding="utf-8") as fp:
-                self.apply_decoding_fix = "LlamaTokenizer" in json.load(fp)["tokenizer_class"]
+                self.apply_decoding_fix = "LlamaTokenizer" in (json.load(fp).get("tokenizer_class") or "")
 
     @property
     def vocab_size(self) -> int:
diff --git a/tests/test_tokenizer.py b/tests/test_tokenizer.py
index c950de6043..95b52423f7 100644
--- a/tests/test_tokenizer.py
+++ b/tests/test_tokenizer.py
@@ -1,4 +1,5 @@
 # Copyright Lightning AI. Licensed under the Apache License 2.0, see LICENSE file.
+import json
 import os
 import shutil
 from pathlib import Path
@@ -112,6 +113,16 @@ def test_tokenizer_input_validation():
         Tokenizer("cocofruit")
 
 
+def test_tokenizer_config_without_tokenizer_class(tmp_path):
+    HFTokenizer(BPE()).save(str(tmp_path / "tokenizer.json"))
+    with open(tmp_path / "tokenizer_config.json", "w", encoding="utf-8") as fp:
+        json.dump({"add_bos_token": False}, fp)
+
+    tokenizer = Tokenizer(tmp_path)
+
+    assert tokenizer.apply_decoding_fix is False
+
+
 @pytest.mark.parametrize("use_bos_by_default", (True, False))
 @pytest.mark.parametrize("encode_use_bos", (None, True, False))
 @pytest.mark.parametrize("encode_use_eos", (True, False))