diff --git a/src/sparse_dot_topn_core/include/sparse_dot_topn/maxheap.hpp b/src/sparse_dot_topn_core/include/sparse_dot_topn/maxheap.hpp
index 2d07ce8..5a3bbe5 100644
--- a/src/sparse_dot_topn_core/include/sparse_dot_topn/maxheap.hpp
+++ b/src/sparse_dot_topn_core/include/sparse_dot_topn/maxheap.hpp
@@ -59,7 +59,7 @@ class MaxHeap {
      * \param initial initial `val` to set for all the entries
      */
     explicit MaxHeap(int n, eT initial) : heap_size{n}, init{initial} {
-        heap.reserve(n);
+        heap.reserve(n + 1);
         for (int i = 0; i < heap_size; i++) {
             heap.push_back({max_order, -1, initial});
         }