diff --git a/onmt/transforms/filtering.py b/onmt/transforms/filtering.py
index f0877741..24badaa3 100644
--- a/onmt/transforms/filtering.py
+++ b/onmt/transforms/filtering.py
@@ -68,7 +68,7 @@ def _parse_opts(self):
         self.word_ratio_threshold = self.opts.word_ratio_threshold
 
     def apply(self, example, **kwargs):
-        """Return None if too long else return as is."""
+        """Return None if the word length ratio is smaller than the threshold."""
         src_len = len(example['src'].split())
         tgt_len = len(example['tgt'].split())
         lengths = sorted([src_len, tgt_len])