diff --git a/gensim/summarization/bm25.py b/gensim/summarization/bm25.py
index 1fb11a8d77..bd4d70911a 100644
--- a/gensim/summarization/bm25.py
+++ b/gensim/summarization/bm25.py
@@ -49,7 +49,7 @@ def get_score(self, document, index, average_idf):
                 continue
             idf = self.idf[word] if self.idf[word] >= 0 else EPSILON * average_idf
             score += (idf * self.f[index][word] * (PARAM_K1 + 1)
-                      / (self.f[index][word] + PARAM_K1 * (1 - PARAM_B + PARAM_B * self.corpus_size / self.avgdl)))
+                      / (self.f[index][word] + PARAM_K1 * (1 - PARAM_B + PARAM_B * len(document) / self.avgdl)))
         return score
 
     def get_scores(self, document, average_idf):