diff --git a/deepspeech/utils/error_rate.py b/deepspeech/utils/error_rate.py
index 6fd593eb..81f458b6 100644
--- a/deepspeech/utils/error_rate.py
+++ b/deepspeech/utils/error_rate.py
@@ -19,6 +19,8 @@ import numpy as np
 
 __all__ = ['word_errors', 'char_errors', 'wer', 'cer']
 
+editdistance.eval("a", "b")
+
 
 def _levenshtein_distance(ref, hyp):
     """Levenshtein distance is a string metric for measuring the difference
@@ -90,6 +92,7 @@ def word_errors(reference, hypothesis, ignore_case=False, delimiter=' '):
     hyp_words = list(filter(None, hypothesis.split(delimiter)))
 
     edit_distance = _levenshtein_distance(ref_words, hyp_words)
+    # `editdistance.eavl precision` less than `_levenshtein_distance`
     # edit_distance = editdistance.eval(ref_words, hyp_words)
     return float(edit_distance), len(ref_words)
 
@@ -121,6 +124,7 @@ def char_errors(reference, hypothesis, ignore_case=False, remove_space=False):
     hypothesis = join_char.join(list(filter(None, hypothesis.split(' '))))
 
     edit_distance = _levenshtein_distance(reference, hypothesis)
+    # `editdistance.eavl precision` less than `_levenshtein_distance`
     # edit_distance = editdistance.eval(reference, hypothesis)
     return float(edit_distance), len(reference)
 
diff --git a/requirements.txt b/requirements.txt
index 9ecf6bbd..332b5238 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -1,4 +1,5 @@
 coverage
+editdistance
 gpustat
 jsonlines
 kaldiio
@@ -19,4 +20,3 @@ tqdm
 typeguard
 visualdl==2.2.0
 yacs
-editdistance
\ No newline at end of file