diff --git a/src/validation.cpp b/src/validation.cpp
--- a/src/validation.cpp
+++ b/src/validation.cpp
@@ -4986,60 +4986,70 @@
 }
 
 bool CChainState::RewindBlockIndex(const Config &config) {
-    LOCK(cs_main);
+    const CChainParams &params = config.GetChainParams();
+
+    int nHeight = 1;
+    CBlockIndex *tip;
 
     // Reduce validity flag and have-data flags.
     // We do this after actual disconnecting, otherwise we'll end up writing the
     // lack of data to disk before writing the chainstate, resulting in a
     // failure to continue if interrupted.
-    for (const auto &entry : mapBlockIndex) {
-        CBlockIndex *pindexIter = entry.second;
-        if (pindexIter->IsValid(BlockValidity::TRANSACTIONS) &&
-            pindexIter->HaveTxsDownloaded()) {
-            setBlockIndexCandidates.insert(pindexIter);
+    {
+        LOCK(cs_main);
+        for (const auto &entry : mapBlockIndex) {
+            CBlockIndex *pindexIter = entry.second;
+            if (pindexIter->IsValid(BlockValidity::TRANSACTIONS) &&
+                pindexIter->HaveTxsDownloaded()) {
+                setBlockIndexCandidates.insert(pindexIter);
+            }
         }
-    }
 
-    const CChainParams &params = config.GetChainParams();
-    int nHeight = chainActive.Height() + 1;
+        nHeight = chainActive.Height() + 1;
+        // nHeight is now the height of the first insufficiently-validated
+        // block, or tipheight + 1
+
+        tip = chainActive.Tip();
+    }
 
-    // nHeight is now the height of the first insufficiently-validated block, or
-    // tipheight + 1
     CValidationState state;
-    CBlockIndex *tip = chainActive.Tip();
     // Loop until the tip is below nHeight, or we reach a pruned block.
     while (true) {
-        // Make sure nothing changed from under us (this won't happen because
-        // RewindBlockIndex runs before importing/network are active)
-        assert(tip == chainActive.Tip());
-        if (tip == nullptr || tip->nHeight < nHeight) break;
-        if (fPruneMode && !chainActive.Tip()->nStatus.hasData()) {
-            // If pruning, don't try rewinding past the HAVE_DATA point; since
-            // older blocks can't be served anyway, there's no need to walk
-            // further, and trying to DisconnectTip() will fail (and require a
-            // needless reindex/redownload of the blockchain).
-            break;
-        }
+        {
+            LOCK(cs_main);
 
-        // Disconnect block
-        if (!DisconnectTip(config, state, nullptr)) {
-            return error("RewindBlockIndex: unable to disconnect block at "
-                         "height %i (%s)",
-                         tip->nHeight, FormatStateMessage(state));
-        }
+            // Make sure nothing changed from under us (this won't happen
+            // because RewindBlockIndex runs before importing/network are
+            // active)
+            assert(tip == chainActive.Tip());
+            if (tip == nullptr || tip->nHeight < nHeight) break;
+            if (fPruneMode && !chainActive.Tip()->nStatus.hasData()) {
+                // If pruning, don't try rewinding past the HAVE_DATA point;
+                // since older blocks can't be served anyway, there's no need to
+                // walk further, and trying to DisconnectTip() will fail (and
+                // require a needless reindex/redownload of the blockchain).
+                break;
+            }
 
-        // Reduce validity flag and have-data flags.
-        // We do this after actual disconnecting, otherwise we'll end up writing
-        // the lack of data to disk before writing the chainstate, resulting in
-        // a failure to continue if interrupted. Note: If we encounter an
-        // insufficiently validated block that is on chainActive, it must be
-        // because we are a pruning node, and this block or some successor
-        // doesn't HAVE_DATA, so we were unable to rewind all the way.  Blocks
-        // remaining on chainActive at this point must not have their validity
-        // reduced.
-        EraseBlockData(tip);
+            // Disconnect block
+            if (!DisconnectTip(config, state, nullptr)) {
+                return error("RewindBlockIndex: unable to disconnect block at "
+                             "height %i (%s)",
+                             tip->nHeight, FormatStateMessage(state));
+            }
 
-        tip = tip->pprev;
+            // Reduce validity flag and have-data flags.
+            // We do this after actual disconnecting, otherwise we'll end up
+            // writing the lack of data to disk before writing the chainstate,
+            // resulting in a failure to continue if interrupted. Note: If we
+            // encounter an insufficiently validated block that is on
+            // chainActive, it must be because we are a pruning node, and this
+            // block or some successor doesn't HAVE_DATA, so we were unable to
+            // rewind all the way.  Blocks remaining on chainActive at this
+            // point must not have their validity reduced.
+            EraseBlockData(tip);
+            tip = tip->pprev;
+        }
 
         // Occasionally flush state to disk.
         if (!FlushStateToDisk(params, state, FlushStateMode::PERIODIC)) {
@@ -5049,12 +5059,15 @@
         }
     }
 
-    if (chainActive.Tip() != nullptr) {
-        // We can't prune block index candidates based on our tip if we have
-        // no tip due to chainActive being empty!
-        PruneBlockIndexCandidates();
+    {
+        LOCK(cs_main);
+        if (chainActive.Tip() != nullptr) {
+            // We can't prune block index candidates based on our tip if we have
+            // no tip due to chainActive being empty!
+            PruneBlockIndexCandidates();
 
-        CheckBlockIndex(params.GetConsensus());
+            CheckBlockIndex(params.GetConsensus());
+        }
     }
 
     return true;