diff --git a/examples/p_bench.cc b/examples/p_bench.cc
index bcdc0a6..5a02719 100644
--- a/examples/p_bench.cc
+++ b/examples/p_bench.cc
@@ -118,6 +118,7 @@ void renumber(const std::vector< uint64_t > & vertex_ids,
     threadpool pool((supports_parallel_insertion) ? num_threads : 1);
 
     stopwatch.start();
+    new_ids.reserve(vertex_ids.size() * 110 / 100);
     pool.parallel_for(vertex_ids.size(), [&](uint64_t i){
         auto id = new_id++;
         new_ids[vertex_ids[i]] = id;