diff --git a/src/chain.h b/src/chain.h
--- a/src/chain.h
+++ b/src/chain.h
@@ -262,9 +262,9 @@
     }
 };
 
-typedef std::unordered_map<BlockHash, CBlockIndex *, BlockHasher> BlockMap;
-extern BlockMap &mapBlockIndex;
 extern CCriticalSection cs_main;
+typedef std::unordered_map<BlockHash, CBlockIndex *, BlockHasher> BlockMap;
+extern BlockMap &mapBlockIndex GUARDED_BY(cs_main);
 
 inline CBlockIndex *LookupBlockIndex(const BlockHash &hash) {
     AssertLockHeld(cs_main);
diff --git a/src/validation.h b/src/validation.h
--- a/src/validation.h
+++ b/src/validation.h
@@ -425,7 +425,7 @@
 /**
  * Mark one block file as pruned.
  */
-void PruneOneBlockFile(const int fileNumber);
+void PruneOneBlockFile(const int fileNumber) EXCLUSIVE_LOCKS_REQUIRED(cs_main);
 
 /**
  * Actually unlink the specified files
diff --git a/src/validation.cpp b/src/validation.cpp
--- a/src/validation.cpp
+++ b/src/validation.cpp
@@ -124,7 +124,7 @@
 
 public:
     CChain chainActive;
-    BlockMap mapBlockIndex;
+    BlockMap mapBlockIndex GUARDED_BY(cs_main);
     std::multimap<CBlockIndex *, CBlockIndex *> mapBlocksUnlinked;
     CBlockIndex *pindexBestInvalid = nullptr;
     CBlockIndex *pindexBestParked = nullptr;
diff --git a/src/wallet/test/wallet_tests.cpp b/src/wallet/test/wallet_tests.cpp
--- a/src/wallet/test/wallet_tests.cpp
+++ b/src/wallet/test/wallet_tests.cpp
@@ -33,6 +33,8 @@
     wallet.AddKeyPubKey(key, key.GetPubKey());
 }
 
+// Note: when backporting PR14957, see PR15321 and ensure both LockAnnotations
+// are in place.
 BOOST_FIXTURE_TEST_CASE(rescan, TestChain100Setup) {
     auto chain = interfaces::MakeChain();
 
@@ -43,6 +45,7 @@
     CreateAndProcessBlock({}, GetScriptForRawPubKey(coinbaseKey.GetPubKey()));
     CBlockIndex *newTip = chainActive.Tip();
 
+    LockAnnotation lock(::cs_main);
     auto locked_chain = chain->lock();
 
     // Verify ScanForWalletTransactions picks up transactions in both the old
@@ -235,6 +238,7 @@
     SetMockTime(mockTime);
     CBlockIndex *block = nullptr;
     if (blockTime > 0) {
+        LockAnnotation lock(::cs_main);
         auto locked_chain = wallet.chain().lock();
         auto inserted =
             mapBlockIndex.emplace(BlockHash(GetRandHash()), new CBlockIndex);