diff --git a/src/cryptonote_core/blockchain.cpp b/src/cryptonote_core/blockchain.cpp
index 19cc90b61..f3105114e 100644
--- a/src/cryptonote_core/blockchain.cpp
+++ b/src/cryptonote_core/blockchain.cpp
@@ -831,6 +831,7 @@ difficulty_type Blockchain::get_difficulty_for_next_block()
   std::vector<uint64_t> timestamps;
   std::vector<difficulty_type> difficulties;
   auto height = m_db->height();
+  top_hash = get_tail_id(); // get it again now that we have the lock
   // ND: Speedup
   // 1. Keep a list of the last 735 (or less) blocks that is used to compute difficulty,
   //    then when the next block difficulty is queried, push the latest height data and
@@ -853,7 +854,7 @@ difficulty_type Blockchain::get_difficulty_for_next_block()
   }
   else
   {
-    size_t offset = height - std::min < size_t > (height, static_cast<size_t>(DIFFICULTY_BLOCKS_COUNT));
+    uint64_t offset = height - std::min <uint64_t> (height, static_cast<uint64_t>(DIFFICULTY_BLOCKS_COUNT));
     if (offset == 0)
       ++offset;