diff --git a/soynlp/utils/utils.py b/soynlp/utils/utils.py
index e02775fe..d9bbffe7 100644
--- a/soynlp/utils/utils.py
+++ b/soynlp/utils/utils.py
@@ -224,6 +224,7 @@ def _counting_from_sents(self, sents):
         check_corpus(sents)
 
         _counter = {}
+        i_sent = -1
         for i_sent, sent in enumerate(sents):
             sent = self.preprocess(sent)
             # filtering during eojeol counting