diff --git a/docs/src/auto_examples/core/run_core_concepts.ipynb b/docs/src/auto_examples/core/run_core_concepts.ipynb
index a1fb7857da..d12965ff7d 100644
--- a/docs/src/auto_examples/core/run_core_concepts.ipynb
+++ b/docs/src/auto_examples/core/run_core_concepts.ipynb
@@ -195,7 +195,7 @@
       },
       "outputs": [],
       "source": [
-        "from gensim import similarities\n\nindex = similarities.SparseMatrixSimilarity(tfidf[bow_corpus], num_features=12)"
+        "from gensim import similarities\n\nindex = similarities.SparseMatrixSimilarity(tfidf[bow_corpus], num_features=max(tfidf.dfs) + 1)"
       ]
     },
     {
@@ -274,4 +274,4 @@
   },
   "nbformat": 4,
   "nbformat_minor": 0
-}
\ No newline at end of file
+}