diff --git a/src/rpc/blockchain.cpp b/src/rpc/blockchain.cpp
--- a/src/rpc/blockchain.cpp
+++ b/src/rpc/blockchain.cpp
@@ -1638,15 +1638,15 @@
     const BlockHash hash(uint256S(strHash));
     CValidationState state;
 
+    CBlockIndex *pblockindex;
     {
         LOCK(cs_main);
-        CBlockIndex *pblockindex = LookupBlockIndex(hash);
+        pblockindex = LookupBlockIndex(hash);
         if (!pblockindex) {
             throw JSONRPCError(RPC_INVALID_ADDRESS_OR_KEY, "Block not found");
         }
-
-        InvalidateBlock(config, state, pblockindex);
     }
+    InvalidateBlock(config, state, pblockindex);
 
     if (state.IsValid()) {
         ActivateBestChain(config, state);
diff --git a/src/validation.h b/src/validation.h
--- a/src/validation.h
+++ b/src/validation.h
@@ -642,7 +642,7 @@
 
 /** Mark a block as invalid. */
 bool InvalidateBlock(const Config &config, CValidationState &state,
-                     CBlockIndex *pindex) EXCLUSIVE_LOCKS_REQUIRED(cs_main);
+                     CBlockIndex *pindex);
 
 /** Park a block. */
 bool ParkBlock(const Config &config, CValidationState &state,
diff --git a/src/validation.cpp b/src/validation.cpp
--- a/src/validation.cpp
+++ b/src/validation.cpp
@@ -3161,6 +3161,7 @@
 
 bool InvalidateBlock(const Config &config, CValidationState &state,
                      CBlockIndex *pindex) {
+    LOCK(cs_main);
     return g_chainstate.UnwindBlock(config, state, pindex, true);
 }