2 files changed, 6 insertions, 1 deletions
diff --git a/src/node/blockstorage.cpp b/src/node/blockstorage.cpp
index cbfdcb6f11..526100f1b2 100644
--- a/src/node/blockstorage.cpp
+++ b/src/node/blockstorage.cpp
@@ -712,6 +712,7 @@ static bool WriteBlockToDisk(const CBlock& block, FlatFilePos& pos, const CMessa
 
 bool BlockManager::WriteUndoDataForBlock(const CBlockUndo& blockundo, BlockValidationState& state, CBlockIndex* pindex, const CChainParams& chainparams)
 {
+    AssertLockHeld(::cs_main);
     // Write undo information to disk
     if (pindex->GetUndoPos().IsNull()) {
         FlatFilePos _pos;
diff --git a/src/node/blockstorage.h b/src/node/blockstorage.h
index 78c9210892..69c97f5d56 100644
--- a/src/node/blockstorage.h
+++ b/src/node/blockstorage.h
@@ -7,12 +7,15 @@
 
 #include <fs.h>
 #include <protocol.h> // For CMessageHeader::MessageStartChars
+#include <sync.h>
 #include <txdb.h>
 
 #include <atomic>
 #include <cstdint>
 #include <vector>
 
+extern RecursiveMutex cs_main;
+
 class ArgsManager;
 class BlockValidationState;
 class CBlock;
@@ -146,7 +149,8 @@ public:
     /** Get block file info entry for one block file */
     CBlockFileInfo* GetBlockFileInfo(size_t n);
 
-    bool WriteUndoDataForBlock(const CBlockUndo& blockundo, BlockValidationState& state, CBlockIndex* pindex, const CChainParams& chainparams);
+    bool WriteUndoDataForBlock(const CBlockUndo& blockundo, BlockValidationState& state, CBlockIndex* pindex, const CChainParams& chainparams)
+        EXCLUSIVE_LOCKS_REQUIRED(::cs_main);
 
     FlatFilePos SaveBlockToDisk(const CBlock& block, int nHeight, CChain& active_chain, const CChainParams& chainparams, const FlatFilePos* dbp);