diff --git a/src/cryptonote_core/tx_pool.cpp b/src/cryptonote_core/tx_pool.cpp
index 7b98acb63..543faa920 100644
--- a/src/cryptonote_core/tx_pool.cpp
+++ b/src/cryptonote_core/tx_pool.cpp
@@ -859,6 +859,9 @@ namespace cryptonote
     std::unordered_set<crypto::key_image> k_images;
 
     LOG_PRINT_L2("Filling block template, median size " << median_size << ", " << m_txs_by_fee_and_receive_time.size() << " txes in the pool");
+
+    LockedTXN lock(m_blockchain);
+
     auto sorted_it = m_txs_by_fee_and_receive_time.begin();
     while (sorted_it != m_txs_by_fee_and_receive_time.end())
     {