diff --git a/src/chainparams.cpp b/src/chainparams.cpp
index c7c6fae8e8..3c4f42cffa 100644
--- a/src/chainparams.cpp
+++ b/src/chainparams.cpp
@@ -56,6 +56,12 @@ public:
         consensus.BIP34Height = 227931;
         consensus.BIP34Hash = uint256S("0x000000000000024b89b42a942fe0d9fea3bb44ab7bd1b19115dd6a759c0808b8");
         consensus.powLimit = uint256S("00000000ffffffffffffffffffffffffffffffffffffffffffffffffffffffff");
+        // Peg-ins Bitcoin headers must have higher difficulty target than this field
+        // This value must be sufficiently small to not preclude realistic parent
+        // chain difficulty during network lifespan yet sufficiently large to
+        // deny peg-in DoS attacks due to our inability to ban after failed
+        // IsBitcoinBlock RPC checks.
+        consensus.parentChainPowLimit = uint256S("00000000ffffffffffffffffffffffffffffffffffffffffffffffffffffffff");
         consensus.nPowTargetTimespan = 14 * 24 * 60 * 60; // two weeks
         consensus.nPowTargetSpacing = 10 * 60;
         consensus.fPowAllowMinDifficultyBlocks = false;
@@ -153,6 +159,7 @@ public:
         consensus.BIP34Height = -1; // BIP34 has not necessarily activated on regtest
         consensus.BIP34Hash = uint256();
         consensus.powLimit = uint256S("7fffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffff");
+        consensus.parentChainPowLimit = uint256S("7fffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffff");
         consensus.nPowTargetTimespan = 14 * 24 * 60 * 60; // two weeks
         consensus.nPowTargetSpacing = 10 * 60;
         consensus.fPowAllowMinDifficultyBlocks = true;
diff --git a/src/consensus/params.h b/src/consensus/params.h
index d97017d0c4..ed295b493b 100644
--- a/src/consensus/params.h
+++ b/src/consensus/params.h
@@ -56,6 +56,7 @@ struct Params {
     BIP9Deployment vDeployments[MAX_VERSION_BITS_DEPLOYMENTS];
     /** Proof of work parameters */
     uint256 powLimit;
+    uint256 parentChainPowLimit;
     bool fPowAllowMinDifficultyBlocks;
     bool fPowNoRetargeting;
     int64_t nPowTargetSpacing;
diff --git a/src/pow.cpp b/src/pow.cpp
index 1593e491d6..140718d58d 100644
--- a/src/pow.cpp
+++ b/src/pow.cpp
@@ -48,7 +48,7 @@ bool CheckBitcoinProof(const CBlockHeader& block)
     bnTarget.SetCompact(block.bitcoinproof.challenge, &fNegative, &fOverflow);
 
     // Check range
-    if (fNegative || bnTarget == 0 || fOverflow || bnTarget > UintToArith256(Params().GetConsensus().powLimit))
+    if (fNegative || bnTarget == 0 || fOverflow || bnTarget > UintToArith256(Params().GetConsensus().parentChainPowLimit))
         return false;
 
     // Check proof of work matches claimed amount