diff --git a/src/chain.h b/src/chain.h
--- a/src/chain.h
+++ b/src/chain.h
@@ -195,11 +195,8 @@
     /** Set/initialize a chain with a given tip. */
     void SetTip(CBlockIndex *pindex);
 
-    /**
-     * Return a CBlockLocator that refers to a block in this chain (by default
-     * the tip).
-     */
-    CBlockLocator GetLocator(const CBlockIndex *pindex = nullptr) const;
+    /** Return a CBlockLocator that refers to the tip of this chain */
+    CBlockLocator GetLocator() const;
 
     /**
      * Find the last common block between this chain and a block index entry.
@@ -213,4 +210,10 @@
     CBlockIndex *FindEarliestAtLeast(int64_t nTime, int height) const;
 };
 
+/** Get a locator for a block index entry. */
+CBlockLocator GetLocator(const CBlockIndex *index);
+
+/** Construct a list of hash entries to put in a locator.  */
+std::vector<BlockHash> LocatorEntries(const CBlockIndex *index);
+
 #endif // BITCOIN_CHAIN_H
diff --git a/src/chain.cpp b/src/chain.cpp
--- a/src/chain.cpp
+++ b/src/chain.cpp
@@ -18,35 +18,36 @@
     }
 }
 
-CBlockLocator CChain::GetLocator(const CBlockIndex *pindex) const {
-    int nStep = 1;
-    std::vector<BlockHash> vHave;
-    vHave.reserve(32);
-
-    if (!pindex) {
-        pindex = Tip();
+std::vector<BlockHash> LocatorEntries(const CBlockIndex *index) {
+    int step = 1;
+    std::vector<BlockHash> have;
+    if (index == nullptr) {
+        return have;
     }
-    while (pindex) {
-        vHave.push_back(pindex->GetBlockHash());
-        // Stop when we have added the genesis block.
-        if (pindex->nHeight == 0) {
+
+    have.reserve(32);
+    while (index) {
+        have.emplace_back(index->GetBlockHash());
+        if (index->nHeight == 0) {
             break;
         }
         // Exponentially larger steps back, plus the genesis block.
-        int nHeight = std::max(pindex->nHeight - nStep, 0);
-        if (Contains(pindex)) {
-            // Use O(1) CChain index if possible.
-            pindex = (*this)[nHeight];
-        } else {
-            // Otherwise, use O(log n) skiplist.
-            pindex = pindex->GetAncestor(nHeight);
-        }
-        if (vHave.size() > 10) {
-            nStep *= 2;
+        int height = std::max(index->nHeight - step, 0);
+        // Use skiplist.
+        index = index->GetAncestor(height);
+        if (have.size() > 10) {
+            step *= 2;
         }
     }
+    return have;
+}
+
+CBlockLocator GetLocator(const CBlockIndex *index) {
+    return CBlockLocator{std::move(LocatorEntries(index))};
+}
 
-    return CBlockLocator(vHave);
+CBlockLocator CChain::GetLocator() const {
+    return ::GetLocator(Tip());
 }
 
 const CBlockIndex *CChain::FindFork(const CBlockIndex *pindex) const {
diff --git a/src/index/base.cpp b/src/index/base.cpp
--- a/src/index/base.cpp
+++ b/src/index/base.cpp
@@ -221,8 +221,7 @@
     if (m_best_block_index == nullptr) {
         return false;
     }
-    GetDB().WriteBestBlock(
-        batch, m_chainstate->m_chain.GetLocator(m_best_block_index));
+    GetDB().WriteBestBlock(batch, GetLocator(m_best_block_index));
     return true;
 }
 
diff --git a/src/net_processing.cpp b/src/net_processing.cpp
--- a/src/net_processing.cpp
+++ b/src/net_processing.cpp
@@ -3251,10 +3251,8 @@
 
     nodestate->nUnconnectingHeaders++;
     // Try to fill in the missing headers.
-    if (MaybeSendGetHeaders(
-            pfrom,
-            m_chainman.ActiveChain().GetLocator(m_chainman.m_best_header),
-            peer)) {
+    if (MaybeSendGetHeaders(pfrom, GetLocator(m_chainman.m_best_header),
+                            peer)) {
         LogPrint(
             BCLog::NET,
             "received header %s: missing prev block %s, sending getheaders "
@@ -3510,13 +3508,12 @@
             return;
         }
     }
+    Assume(pindexLast);
 
     // Consider fetching more headers.
     if (nCount == MAX_HEADERS_RESULTS) {
-        LOCK(cs_main);
         // Headers message had its maximum size; the peer may have more headers.
-        if (MaybeSendGetHeaders(
-                pfrom, m_chainman.ActiveChain().GetLocator(pindexLast), peer)) {
+        if (MaybeSendGetHeaders(pfrom, GetLocator(pindexLast), peer)) {
             LogPrint(
                 BCLog::NET,
                 "more getheaders (%d) to end to peer=%d (startheight:%d)\n",
@@ -4527,10 +4524,8 @@
             if (state.fSyncStarted ||
                 (!peer->m_inv_triggered_getheaders_before_sync &&
                  *best_block != m_last_block_inv_triggering_headers_sync)) {
-                if (MaybeSendGetHeaders(pfrom,
-                                        m_chainman.ActiveChain().GetLocator(
-                                            m_chainman.m_best_header),
-                                        *peer)) {
+                if (MaybeSendGetHeaders(
+                        pfrom, GetLocator(m_chainman.m_best_header), *peer)) {
                     LogPrint(BCLog::NET, "getheaders (%d) %s to peer=%d\n",
                              m_chainman.m_best_header->nHeight,
                              best_block->ToString(), pfrom.GetId());
@@ -5017,10 +5012,8 @@
                 // Doesn't connect (or is genesis), instead of DoSing in
                 // AcceptBlockHeader, request deeper headers
                 if (!m_chainman.ActiveChainstate().IsInitialBlockDownload()) {
-                    MaybeSendGetHeaders(pfrom,
-                                        m_chainman.ActiveChain().GetLocator(
-                                            m_chainman.m_best_header),
-                                        *peer);
+                    MaybeSendGetHeaders(
+                        pfrom, GetLocator(m_chainman.m_best_header), *peer);
                 }
                 return;
             }
@@ -6592,9 +6585,7 @@
                 // getheaders in-flight already, in which case the peer should
                 // still respond to us with a sufficiently high work chain tip.
                 MaybeSendGetHeaders(
-                    pto,
-                    m_chainman.ActiveChain().GetLocator(
-                        state.m_chain_sync.m_work_header->pprev),
+                    pto, GetLocator(state.m_chain_sync.m_work_header->pprev),
                     peer);
                 LogPrint(
                     BCLog::NET,
@@ -7117,9 +7108,7 @@
                 if (pindexStart->pprev) {
                     pindexStart = pindexStart->pprev;
                 }
-                if (MaybeSendGetHeaders(
-                        *pto, m_chainman.ActiveChain().GetLocator(pindexStart),
-                        *peer)) {
+                if (MaybeSendGetHeaders(*pto, GetLocator(pindexStart), *peer)) {
                     LogPrint(
                         BCLog::NET,
                         "initial getheaders (%d) to peer=%d (startheight:%d)\n",
diff --git a/src/node/interfaces.cpp b/src/node/interfaces.cpp
--- a/src/node/interfaces.cpp
+++ b/src/node/interfaces.cpp
@@ -388,6 +388,7 @@
         if (block.m_in_active_chain) {
             *block.m_in_active_chain = active[index->nHeight] == index;
         }
+        // TODO backport core#25494 with change from core#25717
         if (block.m_next_block) {
             FillBlock(active[index->nHeight] == index
                           ? active[index->nHeight + 1]
@@ -536,6 +537,7 @@
             const CChain &active = Assert(m_node.chainman)->ActiveChain();
             return active.GetLocator();
         }
+        // TODO: backport core#25036 with changes from core#25717
         std::optional<int>
         findLocatorFork(const CBlockLocator &locator) override {
             LOCK(cs_main);
diff --git a/src/test/skiplist_tests.cpp b/src/test/skiplist_tests.cpp
--- a/src/test/skiplist_tests.cpp
+++ b/src/test/skiplist_tests.cpp
@@ -92,7 +92,7 @@
         int r = InsecureRandRange(150000);
         CBlockIndex *tip =
             (r < 100000) ? &vBlocksMain[r] : &vBlocksSide[r - 100000];
-        CBlockLocator locator = chain.GetLocator(tip);
+        CBlockLocator locator = GetLocator(tip);
 
         // The first result must be the block itself, the last one must be
         // genesis.