diff --git a/examples/run_lm_finetuning.py b/examples/run_lm_finetuning.py
index 3116faed671..571bcb43919 100644
--- a/examples/run_lm_finetuning.py
+++ b/examples/run_lm_finetuning.py
@@ -66,7 +66,7 @@ class TextDataset(Dataset):
     def __init__(self, tokenizer, file_path='train', block_size=512):
         assert os.path.isfile(file_path)
         directory, filename = os.path.split(file_path)
-        cached_features_file = os.path.join(directory, 'cached_lm_' + block_size + '_' + filename)
+        cached_features_file = os.path.join(directory, 'cached_lm_' + str(block_size) + '_' + filename)
 
         if os.path.exists(cached_features_file):
             logger.info("Loading features from cached file %s", cached_features_file)