diff --git a/src/miner.cpp b/src/miner.cpp
index 356374207..436a59262 100644
--- a/src/miner.cpp
+++ b/src/miner.cpp
@@ -893,6 +893,7 @@ static bool ProcessBlockFound(CBlock* pblock)
 
     // Found a solution
     {
+        LOCK(cs_main);
         if (pblock->hashPrevBlock != chainActive.LastTip()->GetBlockHash())
         {
             uint256 hash; int32_t i;
@@ -1136,7 +1137,11 @@ void static RandomXMiner()
 
             // Create new block
             unsigned int nTransactionsUpdatedLast = mempool.GetTransactionsUpdated();
-            CBlockIndex* pindexPrev = chainActive.LastTip();
+            CBlockIndex* pindexPrev;
+            {
+                LOCK(cs_main);
+                pindexPrev = chainActive.LastTip();
+            }
 
             // If we don't have a valid chain tip to work from, wait and try again.
             if (pindexPrev == nullptr) {