diff --git a/gensim/models/tfidfmodel.py b/gensim/models/tfidfmodel.py
index a4cbedcd22..b45d1652a1 100644
--- a/gensim/models/tfidfmodel.py
+++ b/gensim/models/tfidfmodel.py
@@ -390,10 +390,9 @@ def initialize(self, corpus):
         self.num_nnz = numnnz
         self.dfs = dfs
         # and finally compute the idf weights
-        n_features = max(dfs) if dfs else 0
         logger.info(
             "calculating IDF weights for %i documents and %i features (%i matrix non-zeros)",
-            self.num_docs, n_features, self.num_nnz
+            self.num_docs, max(dfs.keys()) + 1 if dfs else 0, self.num_nnz
         )
         self.idfs = precompute_idfs(self.wglobal, self.dfs, self.num_docs)