diff --git a/src/net_processing.cpp b/src/net_processing.cpp
index ccfbb77fc..4374b5be3 100644
--- a/src/net_processing.cpp
+++ b/src/net_processing.cpp
@@ -101,7 +101,7 @@ namespace {
     /** Blocks that are in flight, and that are in the queue to be downloaded. Protected by cs_main. */
     struct QueuedBlock {
         uint256 hash;
-        CBlockIndex* pindex;                                     //!< Optional.
+        const CBlockIndex* pindex;                               //!< Optional.
         bool fValidatedHeaders;                                  //!< Whether this block has validated headers at the time of request.
         std::unique_ptr<PartiallyDownloadedBlock> partialBlock;  //!< Optional, used for CMPCTBLOCK downloads
     };
@@ -156,13 +156,13 @@ struct CNodeState {
     //! List of asynchronously-determined block rejections to notify this peer about.
     std::vector<CBlockReject> rejects;
     //! The best known block we know this peer has announced.
-    CBlockIndex *pindexBestKnownBlock;
+    const CBlockIndex *pindexBestKnownBlock;
     //! The hash of the last unknown block this peer has announced.
     uint256 hashLastUnknownBlock;
     //! The last full block we both have.
-    CBlockIndex *pindexLastCommonBlock;
+    const CBlockIndex *pindexLastCommonBlock;
     //! The best header we have sent our peer.
-    CBlockIndex *pindexBestHeaderSent;
+    const CBlockIndex *pindexBestHeaderSent;
     //! Length of current-streak of unconnecting headers announcements
     int nUnconnectingHeaders;
     //! Whether we've started headers synchronization with this peer.
@@ -331,7 +331,7 @@ bool MarkBlockAsReceived(const uint256& hash) {
 // Requires cs_main.
 // returns false, still setting pit, if the block was already in flight from the same peer
 // pit will only be valid as long as the same cs_main lock is being held
-bool MarkBlockAsInFlight(NodeId nodeid, const uint256& hash, const Consensus::Params& consensusParams, CBlockIndex *pindex = NULL, list<QueuedBlock>::iterator **pit = NULL) {
+bool MarkBlockAsInFlight(NodeId nodeid, const uint256& hash, const Consensus::Params& consensusParams, const CBlockIndex *pindex = NULL, list<QueuedBlock>::iterator **pit = NULL) {
     CNodeState *state = State(nodeid);
     assert(state != NULL);
 
@@ -432,7 +432,7 @@ bool CanDirectFetch(const Consensus::Params &consensusParams)
 }
 
 // Requires cs_main
-bool PeerHasHeader(CNodeState *state, CBlockIndex *pindex)
+bool PeerHasHeader(CNodeState *state, const CBlockIndex *pindex)
 {
     if (state->pindexBestKnownBlock && pindex == state->pindexBestKnownBlock->GetAncestor(pindex->nHeight))
         return true;
@@ -443,7 +443,7 @@ bool PeerHasHeader(CNodeState *state, CBlockIndex *pindex)
 
 /** Find the last common ancestor two blocks have.
  *  Both pa and pb must be non-NULL. */
-CBlockIndex* LastCommonAncestor(CBlockIndex* pa, CBlockIndex* pb) {
+const CBlockIndex* LastCommonAncestor(const CBlockIndex* pa, const CBlockIndex* pb) {
     if (pa->nHeight > pb->nHeight) {
         pa = pa->GetAncestor(pb->nHeight);
     } else if (pb->nHeight > pa->nHeight) {
@@ -462,7 +462,7 @@ CBlockIndex* LastCommonAncestor(CBlockIndex* pa, CBlockIndex* pb) {
 
 /** Update pindexLastCommonBlock and add not-in-flight missing successors to vBlocks, until it has
  *  at most count entries. */
-void FindNextBlocksToDownload(NodeId nodeid, unsigned int count, std::vector<CBlockIndex*>& vBlocks, NodeId& nodeStaller, const Consensus::Params& consensusParams) {
+void FindNextBlocksToDownload(NodeId nodeid, unsigned int count, std::vector<const CBlockIndex*>& vBlocks, NodeId& nodeStaller, const Consensus::Params& consensusParams) {
     if (count == 0)
         return;
 
@@ -490,8 +490,8 @@ void FindNextBlocksToDownload(NodeId nodeid, unsigned int count, std::vector<CBl
     if (state->pindexLastCommonBlock == state->pindexBestKnownBlock)
         return;
 
-    std::vector<CBlockIndex*> vToFetch;
-    CBlockIndex *pindexWalk = state->pindexLastCommonBlock;
+    std::vector<const CBlockIndex*> vToFetch;
+    const CBlockIndex *pindexWalk = state->pindexLastCommonBlock;
     // Never fetch further than the best block we know the peer has, or more than BLOCK_DOWNLOAD_WINDOW + 1 beyond the last
     // linked block we have in common with this peer. The +1 is so we can detect stalling, namely if we would be able to
     // download that next block if the window were 1 larger.
@@ -514,7 +514,7 @@ void FindNextBlocksToDownload(NodeId nodeid, unsigned int count, std::vector<CBl
         // are not yet downloaded and not in flight to vBlocks. In the mean time, update
         // pindexLastCommonBlock as long as all ancestors are already downloaded, or if it's
         // already part of our chain (and therefore don't need it even if pruned).
-        BOOST_FOREACH(CBlockIndex* pindex, vToFetch) {
+        BOOST_FOREACH(const CBlockIndex* pindex, vToFetch) {
             if (!pindex->IsValid(BLOCK_VALID_TREE)) {
                 // We consider the chain that this peer is on invalid.
                 return;
@@ -1049,7 +1049,7 @@ void static ProcessGetData(CNode* pfrom, const Consensus::Params& consensusParam
     }
 }
 
-uint32_t GetFetchFlags(CNode* pfrom, CBlockIndex* pprev, const Consensus::Params& chainparams) {
+uint32_t GetFetchFlags(CNode* pfrom, const CBlockIndex* pprev, const Consensus::Params& chainparams) {
     uint32_t nFetchFlags = 0;
     if ((pfrom->GetLocalServices() & NODE_WITNESS) && State(pfrom->GetId())->fHaveWitness) {
         nFetchFlags |= MSG_WITNESS_FLAG;
@@ -1456,7 +1456,7 @@ bool static ProcessMessage(CNode* pfrom, string strCommand, CDataStream& vRecv,
         LOCK(cs_main);
 
         // Find the last block the caller has in the main chain
-        CBlockIndex* pindex = FindForkInGlobalIndex(chainActive, locator);
+        const CBlockIndex* pindex = FindForkInGlobalIndex(chainActive, locator);
 
         // Send the rest of the chain
         if (pindex)
@@ -1552,7 +1552,7 @@ bool static ProcessMessage(CNode* pfrom, string strCommand, CDataStream& vRecv,
         }
 
         CNodeState *nodestate = State(pfrom->GetId());
-        CBlockIndex* pindex = NULL;
+        const CBlockIndex* pindex = NULL;
         if (locator.IsNull())
         {
             // If locator is null, return the hashStop block
@@ -1775,7 +1775,7 @@ bool static ProcessMessage(CNode* pfrom, string strCommand, CDataStream& vRecv,
         }
         }
 
-        CBlockIndex *pindex = NULL;
+        const CBlockIndex *pindex = NULL;
         CValidationState state;
         if (!ProcessNewBlockHeaders({cmpctblock.header}, state, chainparams, &pindex)) {
             int nDoS;
@@ -2051,7 +2051,7 @@ bool static ProcessMessage(CNode* pfrom, string strCommand, CDataStream& vRecv,
             return true;
         }
 
-        CBlockIndex *pindexLast = NULL;
+        const CBlockIndex *pindexLast = NULL;
         {
         LOCK(cs_main);
         CNodeState *nodestate = State(pfrom->GetId());
@@ -2128,8 +2128,8 @@ bool static ProcessMessage(CNode* pfrom, string strCommand, CDataStream& vRecv,
         // If this set of headers is valid and ends in a block with at least as
         // much work as our tip, download as much as possible.
         if (fCanDirectFetch && pindexLast->IsValid(BLOCK_VALID_TREE) && chainActive.Tip()->nChainWork <= pindexLast->nChainWork) {
-            vector<CBlockIndex *> vToFetch;
-            CBlockIndex *pindexWalk = pindexLast;
+            vector<const CBlockIndex *> vToFetch;
+            const CBlockIndex *pindexWalk = pindexLast;
             // Calculate all the blocks we'd need to switch to pindexLast, up to a limit.
             while (pindexWalk && !chainActive.Contains(pindexWalk) && vToFetch.size() <= MAX_BLOCKS_IN_TRANSIT_PER_PEER) {
                 if (!(pindexWalk->nStatus & BLOCK_HAVE_DATA) &&
@@ -2151,7 +2151,7 @@ bool static ProcessMessage(CNode* pfrom, string strCommand, CDataStream& vRecv,
             } else {
                 vector<CInv> vGetData;
                 // Download as much as possible, from earliest to latest.
-                BOOST_REVERSE_FOREACH(CBlockIndex *pindex, vToFetch) {
+                BOOST_REVERSE_FOREACH(const CBlockIndex *pindex, vToFetch) {
                     if (nodestate->nBlocksInFlight >= MAX_BLOCKS_IN_TRANSIT_PER_PEER) {
                         // Can't download any more from this peer
                         break;
@@ -2740,7 +2740,7 @@ bool SendMessages(CNode* pto, CConnman& connman, std::atomic<bool>& interruptMsg
             bool fRevertToInv = ((!state.fPreferHeaders &&
                                  (!state.fPreferHeaderAndIDs || pto->vBlockHashesToAnnounce.size() > 1)) ||
                                 pto->vBlockHashesToAnnounce.size() > MAX_BLOCKS_TO_ANNOUNCE);
-            CBlockIndex *pBestIndex = NULL; // last header queued for delivery
+            const CBlockIndex *pBestIndex = NULL; // last header queued for delivery
             ProcessBlockAvailability(pto->id); // ensure pindexBestKnownBlock is up-to-date
 
             if (!fRevertToInv) {
@@ -2751,7 +2751,7 @@ bool SendMessages(CNode* pto, CConnman& connman, std::atomic<bool>& interruptMsg
                 BOOST_FOREACH(const uint256 &hash, pto->vBlockHashesToAnnounce) {
                     BlockMap::iterator mi = mapBlockIndex.find(hash);
                     assert(mi != mapBlockIndex.end());
-                    CBlockIndex *pindex = mi->second;
+                    const CBlockIndex *pindex = mi->second;
                     if (chainActive[pindex->nHeight] != pindex) {
                         // Bail out if we reorged away from this block
                         fRevertToInv = true;
@@ -2828,7 +2828,7 @@ bool SendMessages(CNode* pto, CConnman& connman, std::atomic<bool>& interruptMsg
                     const uint256 &hashToAnnounce = pto->vBlockHashesToAnnounce.back();
                     BlockMap::iterator mi = mapBlockIndex.find(hashToAnnounce);
                     assert(mi != mapBlockIndex.end());
-                    CBlockIndex *pindex = mi->second;
+                    const CBlockIndex *pindex = mi->second;
 
                     // Warn if we're announcing a block that is not on the main chain.
                     // This should be very rare and could be optimized out.
@@ -3013,10 +3013,10 @@ bool SendMessages(CNode* pto, CConnman& connman, std::atomic<bool>& interruptMsg
         //
         vector<CInv> vGetData;
         if (!pto->fClient && (fFetch || !IsInitialBlockDownload()) && state.nBlocksInFlight < MAX_BLOCKS_IN_TRANSIT_PER_PEER) {
-            vector<CBlockIndex*> vToDownload;
+            vector<const CBlockIndex*> vToDownload;
             NodeId staller = -1;
             FindNextBlocksToDownload(pto->GetId(), MAX_BLOCKS_IN_TRANSIT_PER_PEER - state.nBlocksInFlight, vToDownload, staller, consensusParams);
-            BOOST_FOREACH(CBlockIndex *pindex, vToDownload) {
+            BOOST_FOREACH(const CBlockIndex *pindex, vToDownload) {
                 uint32_t nFetchFlags = GetFetchFlags(pto, pindex->pprev, consensusParams);
                 vGetData.push_back(CInv(MSG_BLOCK | nFetchFlags, pindex->GetBlockHash()));
                 MarkBlockAsInFlight(pto->GetId(), pindex->GetBlockHash(), consensusParams, pindex);
diff --git a/src/validation.cpp b/src/validation.cpp
index ca1e5a713..a6466334a 100644
--- a/src/validation.cpp
+++ b/src/validation.cpp
@@ -3030,12 +3030,14 @@ static bool AcceptBlockHeader(const CBlockHeader& block, CValidationState& state
 }
 
 // Exposed wrapper for AcceptBlockHeader
-bool ProcessNewBlockHeaders(const std::vector<CBlockHeader>& headers, CValidationState& state, const CChainParams& chainparams, CBlockIndex** ppindex)
+bool ProcessNewBlockHeaders(const std::vector<CBlockHeader>& headers, CValidationState& state, const CChainParams& chainparams, const CBlockIndex** ppindex)
 {
     {
         LOCK(cs_main);
         for (const CBlockHeader& header : headers) {
-            if (!AcceptBlockHeader(header, state, chainparams, ppindex)) {
+            // cast away the ppindex-returns-const CBlockIndex - we're just assigning it to a CBlockIndex*
+            // that we own and is updated non-const anyway
+            if (!AcceptBlockHeader(header, state, chainparams, const_cast<CBlockIndex**>(ppindex))) {
                 return false;
             }
         }
diff --git a/src/validation.h b/src/validation.h
index 981f65963..be49b0e65 100644
--- a/src/validation.h
+++ b/src/validation.h
@@ -243,7 +243,7 @@ bool ProcessNewBlock(const CChainParams& chainparams, const std::shared_ptr<cons
  * @param[in]  chainparams The params for the chain we want to connect to
  * @param[out] ppindex If set, the pointer will be set to point to the last new block index object for the given headers
  */
-bool ProcessNewBlockHeaders(const std::vector<CBlockHeader>& block, CValidationState& state, const CChainParams& chainparams, CBlockIndex** ppindex=NULL);
+bool ProcessNewBlockHeaders(const std::vector<CBlockHeader>& block, CValidationState& state, const CChainParams& chainparams, const CBlockIndex** ppindex=NULL);
 
 /** Check whether enough disk space is available for an incoming block */
 bool CheckDiskSpace(uint64_t nAdditionalBytes = 0);