diff --git a/quiche/quic/core/quic_connection_id_manager.cc b/quiche/quic/core/quic_connection_id_manager.cc
index 74d3a51..0d8ed48 100644
--- a/quiche/quic/core/quic_connection_id_manager.cc
+++ b/quiche/quic/core/quic_connection_id_manager.cc
@@ -235,6 +235,7 @@
 std::vector<uint64_t> QuicPeerIssuedConnectionIdManager::
     ConsumeToBeRetiredConnectionIdSequenceNumbers() {
   std::vector<uint64_t> result;
+  result.reserve(to_be_retired_connection_id_data_.size());
   for (auto const& cid_data : to_be_retired_connection_id_data_) {
     result.push_back(cid_data.sequence_number);
   }