diff --git a/src/Makefile.am b/src/Makefile.am
index d275489d5..df7cee91c 100644
--- a/src/Makefile.am
+++ b/src/Makefile.am
@@ -107,6 +107,7 @@ BITCOIN_CORE_H = \
   addrdb.h \
   addrman.h \
   attributes.h \
+  auxpow.h \
   banman.h \
   base58.h \
   bech32.h \
@@ -489,6 +490,7 @@ libbitcoin_consensus_a_SOURCES = \
 libbitcoin_common_a_CPPFLAGS = $(AM_CPPFLAGS) $(BITCOIN_INCLUDES)
 libbitcoin_common_a_CXXFLAGS = $(AM_CXXFLAGS) $(PIE_FLAGS)
 libbitcoin_common_a_SOURCES = \
+  auxpow.cpp \
   base58.cpp \
   bech32.cpp \
   bloom.cpp \
diff --git a/src/auxpow.cpp b/src/auxpow.cpp
new file mode 100644
index 000000000..eabe723e0
--- /dev/null
+++ b/src/auxpow.cpp
@@ -0,0 +1,216 @@
+// Copyright (c) 2009-2010 Satoshi Nakamoto
+// Copyright (c) 2011 Vince Durham
+// Copyright (c) 2009-2014 The Bitcoin developers
+// Copyright (c) 2014-2019 Daniel Kraft
+// Copyright (c) 2021 The Dogecoin Core developers
+// Distributed under the MIT/X11 software license, see the accompanying
+// file license.txt or http://www.opensource.org/licenses/mit-license.php.
+
+#include <auxpow.h>
+
+#include <consensus/consensus.h>
+#include <consensus/merkle.h>
+#include <hash.h>
+#include <primitives/block.h>
+#include <script/script.h>
+#include <util/strencodings.h>
+#include <util/system.h>
+
+#include <algorithm>
+
+namespace
+{
+
+/**
+ * Decodes a 32-bit little endian integer from raw bytes.
+ */
+uint32_t
+DecodeLE32(const unsigned char* bytes)
+{
+  uint32_t res = 0;
+  for (int i = 0; i < 4; ++i)
+    {
+      res <<= 8;
+      res |= bytes[3 - i];
+    }
+  return res;
+}
+
+} // anonymous namespace
+
+bool
+CAuxPow::check(const uint256& hashAuxBlock, int nChainId,
+                const Consensus::Params& params) const
+{
+    if (params.fStrictChainId && parentBlock.GetChainId() == nChainId)
+        return error("Aux POW parent has our chain ID");
+
+    if (vChainMerkleBranch.size() > 30)
+        return error("Aux POW chain merkle branch too long");
+
+    // Check that the chain merkle root is in the coinbase
+    const uint256 nRootHash
+      = CheckMerkleBranch(hashAuxBlock, vChainMerkleBranch, nChainIndex);
+    std::vector<unsigned char> vchRootHash(nRootHash.begin(), nRootHash.end());
+    std::reverse(vchRootHash.begin(), vchRootHash.end()); // correct endian
+
+    // Check that we are in the parent block merkle tree
+    if (CheckMerkleBranch(coinbaseTx->GetHash(), vMerkleBranch, 0)
+          != parentBlock.hashMerkleRoot)
+        return error("Aux POW merkle root incorrect");
+
+    // Check that there is at least one input.
+    if (coinbaseTx->vin.empty())
+        return error("Aux POW coinbase has no inputs");
+
+    const CScript script = coinbaseTx->vin[0].scriptSig;
+
+    // Check that the same work is not submitted twice to our chain.
+    //
+
+    const unsigned char* const mmHeaderBegin = pchMergedMiningHeader;
+    const unsigned char* const mmHeaderEnd
+        = mmHeaderBegin + sizeof(pchMergedMiningHeader);
+    CScript::const_iterator pcHead =
+        std::search(script.begin(), script.end(), mmHeaderBegin, mmHeaderEnd);
+
+    CScript::const_iterator pc =
+        std::search(script.begin(), script.end(), vchRootHash.begin(), vchRootHash.end());
+
+    if (pc == script.end())
+        return error("Aux POW missing chain merkle root in parent coinbase");
+
+    if (pcHead != script.end())
+    {
+        // Enforce only one chain merkle root by checking that a single instance of the merged
+        // mining header exists just before.
+        if (script.end() != std::search(pcHead + 1, script.end(),
+                                        mmHeaderBegin, mmHeaderEnd))
+            return error("Multiple merged mining headers in coinbase");
+        if (pcHead + sizeof(pchMergedMiningHeader) != pc)
+            return error("Merged mining header is not just before chain merkle root");
+    }
+    else
+    {
+        // For backward compatibility.
+        // Enforce only one chain merkle root by checking that it starts early in the coinbase.
+        // 8-12 bytes are enough to encode extraNonce and nBits.
+        if (pc - script.begin() > 20)
+            return error("Aux POW chain merkle root must start in the first 20 bytes of the parent coinbase");
+    }
+
+
+    // Ensure we are at a deterministic point in the merkle leaves by hashing
+    // a nonce and our chain ID and comparing to the index.
+    pc += vchRootHash.size();
+    if (script.end() - pc < 8)
+        return error("Aux POW missing chain merkle tree size and nonce in parent coinbase");
+
+    const uint32_t nSize = DecodeLE32(&pc[0]);
+    const unsigned merkleHeight = vChainMerkleBranch.size();
+    if (nSize != (1u << merkleHeight))
+        return error("Aux POW merkle branch size does not match parent coinbase");
+
+    const uint32_t nNonce = DecodeLE32(&pc[4]);
+    if (nChainIndex != getExpectedIndex(nNonce, nChainId, merkleHeight))
+        return error("Aux POW wrong index");
+
+    return true;
+}
+
+int
+CAuxPow::getExpectedIndex(uint32_t nNonce, int nChainId, unsigned h)
+{
+  // Choose a pseudo-random slot in the chain merkle tree
+  // but have it be fixed for a size/nonce/chain combination.
+  //
+  // This prevents the same work from being used twice for the
+  // same chain while reducing the chance that two chains clash
+  // for the same slot.
+
+  /* This computation can overflow the uint32 used.  This is not an issue,
+     though, since we take the mod against a power-of-two in the end anyway.
+     This also ensures that the computation is, actually, consistent
+     even if done in 64 bits as it was in the past on some systems.
+
+     Note that h is always <= 30 (enforced by the maximum allowed chain
+     merkle branch length), so that 32 bits are enough for the computation.  */
+
+  uint32_t rand = nNonce;
+  rand = rand * 1103515245 + 12345;
+  rand += nChainId;
+  rand = rand * 1103515245 + 12345;
+
+  return rand % (1u << h);
+}
+
+uint256
+CAuxPow::CheckMerkleBranch(uint256 hash,
+                           const std::vector<uint256>& vMerkleBranch,
+                           int nIndex)
+{
+  if (nIndex == -1)
+    return uint256 ();
+  for (std::vector<uint256>::const_iterator it(vMerkleBranch.begin());
+       it != vMerkleBranch.end(); ++it)
+  {
+    if (nIndex & 1)
+      hash = Hash(*it, hash);
+    else
+      hash = Hash(hash, *it);
+    nIndex >>= 1;
+  }
+  return hash;
+}
+
+std::unique_ptr<CAuxPow>
+CAuxPow::createAuxPow(const CPureBlockHeader& header)
+{
+  assert(header.IsAuxpow());
+
+  /* Build a minimal coinbase script input for merge-mining.  */
+  const uint256 blockHash = header.GetHash();
+  std::vector<unsigned char> inputData(blockHash.begin(), blockHash.end());
+  std::reverse(inputData.begin(), inputData.end());
+  inputData.push_back(1);
+  inputData.insert(inputData.end(), 7, 0);
+
+  /* Fake a parent-block coinbase with just the required input
+     script and no outputs.  */
+  CMutableTransaction coinbase;
+  coinbase.vin.resize(1);
+  coinbase.vin[0].prevout.SetNull();
+  coinbase.vin[0].scriptSig = (CScript () << inputData);
+  assert(coinbase.vout.empty());
+  CTransactionRef coinbaseRef = MakeTransactionRef(coinbase);
+
+  /* Build a fake parent block with the coinbase.  */
+  CBlock parent;
+  parent.nVersion = 1;
+  parent.vtx.resize(1);
+  parent.vtx[0] = coinbaseRef;
+  parent.hashMerkleRoot = BlockMerkleRoot(parent);
+
+  /* Construct the auxpow object.  */
+  std::unique_ptr<CAuxPow> auxpow(new CAuxPow(std::move(coinbaseRef)));
+  assert(auxpow->vMerkleBranch.empty());
+  assert(auxpow->vChainMerkleBranch.empty());
+  auxpow->nChainIndex = 0;
+  auxpow->parentBlock = parent;
+
+  return auxpow;
+}
+
+CPureBlockHeader&
+CAuxPow::initAuxPow(CBlockHeader& header)
+{
+  /* Set auxpow flag right now, since we take the block hash below when creating
+     the minimal auxpow for header.  */
+  header.SetAuxpowFlag(true);
+
+  std::unique_ptr<CAuxPow> apow = createAuxPow(header);
+  CPureBlockHeader& result = apow->parentBlock;
+  header.SetAuxpow(std::move (apow));
+
+  return result;
+}
diff --git a/src/auxpow.h b/src/auxpow.h
new file mode 100644
index 000000000..6e04e8630
--- /dev/null
+++ b/src/auxpow.h
@@ -0,0 +1,158 @@
+// Copyright (c) 2009-2010 Satoshi Nakamoto
+// Copyright (c) 2009-2014 The Bitcoin developers
+// Copyright (c) 2014-2019 Daniel Kraft
+// Distributed under the MIT/X11 software license, see the accompanying
+// file license.txt or http://www.opensource.org/licenses/mit-license.php.
+
+#ifndef BITCOIN_AUXPOW_H
+#define BITCOIN_AUXPOW_H
+
+#include <consensus/params.h>
+#include <primitives/pureheader.h>
+#include <primitives/transaction.h>
+#include <serialize.h>
+#include <uint256.h>
+
+#include <cassert>
+#include <memory>
+#include <vector>
+
+class CBlock;
+class CBlockHeader;
+class CBlockIndex;
+class CValidationState;
+class UniValue;
+
+namespace auxpow_tests
+{
+class CAuxPowForTest;
+}
+
+/** Header for merge-mining data in the coinbase.  */
+static const unsigned char pchMergedMiningHeader[] = { 0xfa, 0xbe, 'm', 'm' };
+
+/**
+ * Data for the merge-mining auxpow.  This uses a merkle tx (the parent block's
+ * coinbase tx) and a second merkle branch to link the actual Namecoin block
+ * header to the parent block header, which is mined to satisfy the PoW.
+ */
+class CAuxPow
+{
+
+private:
+
+  /** The parent block's coinbase transaction.  */
+  CTransactionRef coinbaseTx;
+
+  /** The Merkle branch of the coinbase tx to the parent block's root.  */
+  std::vector<uint256> vMerkleBranch;
+
+  /** The merkle branch connecting the aux block to our coinbase.  */
+  std::vector<uint256> vChainMerkleBranch;
+
+  /** Merkle tree index of the aux block header in the coinbase.  */
+  int nChainIndex;
+
+  /** Parent block header (on which the real PoW is done).  */
+  CPureBlockHeader parentBlock;
+
+  /**
+   * Check a merkle branch.  This used to be in CBlock, but was removed
+   * upstream.  Thus include it here now.
+   */
+  static uint256 CheckMerkleBranch (uint256 hash,
+                                    const std::vector<uint256>& vMerkleBranch,
+                                    int nIndex);
+
+  friend UniValue AuxpowToJSON(const CAuxPow& auxpow);
+  friend class auxpow_tests::CAuxPowForTest;
+
+public:
+
+  /* Prevent accidental conversion.  */
+  inline explicit CAuxPow (CTransactionRef&& txIn)
+    : coinbaseTx (std::move (txIn))
+  {}
+
+  CAuxPow () = default;
+
+  SERIALIZE_METHODS (CAuxPow, obj)
+  {
+    /* The coinbase Merkle tx' hashBlock field is never actually verified
+       or used in the code for an auxpow (and never was).  The parent block
+       is known anyway directly, so this is also redundant.  By setting the
+       value to zero (for serialising), we make sure that the format is
+       backwards compatible but the data can be compressed.  */
+    uint256 hashBlock;
+
+    /* The index of the parent coinbase tx is always zero.  */
+    int nIndex = 0;
+
+    /* Data from the coinbase transaction as Merkle tx.  */
+    READWRITE (obj.coinbaseTx, hashBlock, obj.vMerkleBranch, nIndex);
+
+    /* Additional data for the auxpow itself.  */
+    READWRITE (obj.vChainMerkleBranch, obj.nChainIndex, obj.parentBlock);
+  }
+
+  /**
+   * Check the auxpow, given the merge-mined block's hash and our chain ID.
+   * Note that this does not verify the actual PoW on the parent block!  It
+   * just confirms that all the merkle branches are valid.
+   * @param hashAuxBlock Hash of the merge-mined block.
+   * @param nChainId The auxpow chain ID of the block to check.
+   * @param params Consensus parameters.
+   * @return True if the auxpow is valid.
+   */
+  bool check (const uint256& hashAuxBlock, int nChainId,
+              const Consensus::Params& params) const;
+
+  /**
+   * Returns the parent block hash.  This is used to validate the PoW.
+   */
+  inline uint256
+  getParentBlockPoWHash() const
+  {
+    return parentBlock.GetPoWHash();
+  }
+
+  /**
+   * Return parent block.  This is only used for the temporary parentblock
+   * auxpow version check.
+   * @return The parent block.
+   */
+  /* FIXME: Remove after the hardfork.  */
+  inline const CPureBlockHeader&
+  getParentBlock () const
+  {
+    return parentBlock;
+  }
+
+  /**
+   * Calculate the expected index in the merkle tree.  This is also used
+   * for the test-suite.
+   * @param nNonce The coinbase's nonce value.
+   * @param nChainId The chain ID.
+   * @param h The merkle block height.
+   * @return The expected index for the aux hash.
+   */
+  static int getExpectedIndex (uint32_t nNonce, int nChainId, unsigned h);
+
+  /**
+   * Constructs a minimal CAuxPow object for the given block header and
+   * returns it.  The caller should make sure to set the auxpow flag on the
+   * header already, since the block hash to which the auxpow commits depends
+   * on that!
+   */
+  static std::unique_ptr<CAuxPow> createAuxPow (const CPureBlockHeader& header);
+
+  /**
+   * Initialises the auxpow of the given block header.  This builds a minimal
+   * auxpow object like createAuxPow and sets it on the block header.  Returns
+   * a reference to the parent header so it can be mined as a follow-up.
+   */
+  static CPureBlockHeader& initAuxPow (CBlockHeader& header);
+
+};
+
+#endif // BITCOIN_AUXPOW_H
diff --git a/src/chain.cpp b/src/chain.cpp
index 7ce0d5df1..7a4ce6b09 100644
--- a/src/chain.cpp
+++ b/src/chain.cpp
@@ -5,6 +5,10 @@
 
 #include <chain.h>
 
+// Dogecoin: Include the single function signature we need, to avoid the entire
+// validation.h being pulled in and creating a cyclic include loop
+bool ReadBlockHeaderFromDisk(CBlockHeader& block, const CBlockIndex* pindex, const Consensus::Params& consensusParams, const bool fCheckPOW = true);
+
 /* Moved here from the header, because we need auxpow and the logic
    becomes more involved.  */
 CBlockHeader CBlockIndex::GetBlockHeader(const Consensus::Params& consensusParams, bool fCheckPOW) const
@@ -13,6 +17,15 @@ CBlockHeader CBlockIndex::GetBlockHeader(const Consensus::Params& consensusParam
 
     block.nVersion       = nVersion;
 
+    /* The CBlockIndex object's block header is missing the auxpow.
+       So if this is an auxpow block, read it from disk instead.  We only
+       have to read the actual *header*, not the full block.  */
+    if (block.IsAuxpow())
+    {
+        ReadBlockHeaderFromDisk(block, this, consensusParams, fCheckPOW);
+        return block;
+    }
+
     if (pprev)
         block.hashPrevBlock = pprev->GetBlockHash();
     block.hashMerkleRoot = hashMerkleRoot;
diff --git a/src/primitives/block.cpp b/src/primitives/block.cpp
index c95038d9b..b174ccb26 100644
--- a/src/primitives/block.cpp
+++ b/src/primitives/block.cpp
@@ -10,6 +10,19 @@
 #include <crypto/common.h>
 #include <crypto/scrypt.h>
 
+void CBlockHeader::SetAuxpow (std::unique_ptr<CAuxPow> apow)
+{
+    if (apow != nullptr)
+    {
+        auxpow.reset(apow.release());
+        SetAuxpowFlag(true);
+    } else
+    {
+        auxpow.reset();
+        SetAuxpowFlag(false);
+    }
+}
+
 std::string CBlock::ToString() const
 {
     std::stringstream s;
diff --git a/src/primitives/block.h b/src/primitives/block.h
index d41be19ed..dae194fc4 100644
--- a/src/primitives/block.h
+++ b/src/primitives/block.h
@@ -6,11 +6,14 @@
 #ifndef BITCOIN_PRIMITIVES_BLOCK_H
 #define BITCOIN_PRIMITIVES_BLOCK_H
 
+#include <auxpow.h>
 #include <primitives/transaction.h>
 #include <primitives/pureheader.h>
 #include <serialize.h>
 #include <uint256.h>
 
+#include <memory>
+
 /** Nodes collect new transactions into a block, hash them into a hash tree,
  * and scan through nonce values to make the block's hash satisfy proof-of-work
  * requirements.  When they solve the proof-of-work, they broadcast the block
@@ -22,6 +25,9 @@ class CBlockHeader : public CPureBlockHeader
 {
 public:
 
+    // auxpow (if this is a merge-minded block)
+    std::shared_ptr<CAuxPow> auxpow;
+
     CBlockHeader()
     {
         SetNull();
@@ -30,13 +36,29 @@ public:
     SERIALIZE_METHODS(CBlockHeader, obj)
     {
         READWRITEAS(CPureBlockHeader, obj);
+
+        if (obj.IsAuxpow())
+        {
+            SER_READ(obj, obj.auxpow = std::make_shared<CAuxPow>());
+            assert(obj.auxpow != nullptr);
+            READWRITE(*obj.auxpow);
+        } else
+        {
+            SER_READ(obj, obj.auxpow.reset());
+        }
     }
 
     void SetNull()
     {
         CPureBlockHeader::SetNull();
+        auxpow.reset();
     }
 
+    /**
+     * Set the block's auxpow (or unset it).  This takes care of updating
+     * the version accordingly.
+     */
+    void SetAuxpow (std::unique_ptr<CAuxPow> apow);
 };
 
 
@@ -82,6 +104,7 @@ public:
         block.nTime          = nTime;
         block.nBits          = nBits;
         block.nNonce         = nNonce;
+        block.auxpow         = auxpow;
         return block;
     }