diff --git a/consensus/ethash/consensus.go b/consensus/ethash/consensus.go
index 1c38b80ea..b6e7b9511 100644
--- a/consensus/ethash/consensus.go
+++ b/consensus/ethash/consensus.go
@@ -31,6 +31,7 @@ import (
 	"github.com/ethereum/go-ethereum/consensus/misc"
 	"github.com/ethereum/go-ethereum/core/state"
 	"github.com/ethereum/go-ethereum/core/types"
+	"github.com/ethereum/go-ethereum/log"
 	"github.com/ethereum/go-ethereum/params"
 	"github.com/ethereum/go-ethereum/rlp"
 	"github.com/ethereum/go-ethereum/trie"
@@ -330,7 +331,13 @@ func (ethash *Ethash) verifyHeader(chain consensus.ChainHeaderReader, header, pa
 // the difficulty that a new block should have when created at time
 // given the parent block's time and difficulty.
 func (ethash *Ethash) CalcDifficulty(chain consensus.ChainHeaderReader, time uint64, parent *types.Header) *big.Int {
-	return CalcDifficulty(chain.Config(), time, parent)
+	var config = chain.Config()
+	var ret = CalcDifficulty(config, time, parent)
+	if nil != config.CappedMaximumDifficulty && ret.Cmp(config.CappedMaximumDifficulty) >= 0 {
+		log.Info(fmt.Sprintf("Using capped difficulty %d", config.CappedMaximumDifficulty))
+		return config.CappedMaximumDifficulty
+	}
+	return ret
 }
 
 // CalcDifficulty is the difficulty adjustment algorithm. It returns
diff --git a/params/config.go b/params/config.go
index 80e671f9b..b56a3a606 100644
--- a/params/config.go
+++ b/params/config.go
@@ -270,16 +270,16 @@ var (
 	//
 	// This configuration is intentionally not using keyed fields to force anyone
 	// adding flags to the config to also have to set these fields.
-	AllEthashProtocolChanges = &ChainConfig{big.NewInt(1337), big.NewInt(0), nil, false, big.NewInt(0), common.Hash{}, big.NewInt(0), big.NewInt(0), big.NewInt(0), big.NewInt(0), big.NewInt(0), big.NewInt(0), big.NewInt(0), big.NewInt(0), big.NewInt(0), big.NewInt(0), big.NewInt(0), nil, nil, nil, nil, false, new(EthashConfig), nil}
+	AllEthashProtocolChanges = &ChainConfig{big.NewInt(1337), big.NewInt(0), nil, false, big.NewInt(0), common.Hash{}, big.NewInt(0), big.NewInt(0), big.NewInt(0), big.NewInt(0), big.NewInt(0), big.NewInt(0), big.NewInt(0), big.NewInt(0), big.NewInt(0), big.NewInt(0), big.NewInt(0), nil, nil, nil, nil, nil, false, new(EthashConfig), nil}
 
 	// AllCliqueProtocolChanges contains every protocol change (EIPs) introduced
 	// and accepted by the Ethereum core developers into the Clique consensus.
 	//
 	// This configuration is intentionally not using keyed fields to force anyone
 	// adding flags to the config to also have to set these fields.
-	AllCliqueProtocolChanges = &ChainConfig{big.NewInt(1337), big.NewInt(0), nil, false, big.NewInt(0), common.Hash{}, big.NewInt(0), big.NewInt(0), big.NewInt(0), big.NewInt(0), big.NewInt(0), big.NewInt(0), big.NewInt(0), big.NewInt(0), big.NewInt(0), nil, nil, nil, nil, nil, nil, false, nil, &CliqueConfig{Period: 0, Epoch: 30000}}
+	AllCliqueProtocolChanges = &ChainConfig{big.NewInt(1337), big.NewInt(0), nil, false, big.NewInt(0), common.Hash{}, big.NewInt(0), big.NewInt(0), big.NewInt(0), big.NewInt(0), big.NewInt(0), big.NewInt(0), big.NewInt(0), big.NewInt(0), big.NewInt(0), nil, nil, nil, nil, nil, nil, nil, false, nil, &CliqueConfig{Period: 0, Epoch: 30000}}
 
-	TestChainConfig = &ChainConfig{big.NewInt(1), big.NewInt(0), nil, false, big.NewInt(0), common.Hash{}, big.NewInt(0), big.NewInt(0), big.NewInt(0), big.NewInt(0), big.NewInt(0), big.NewInt(0), big.NewInt(0), big.NewInt(0), big.NewInt(0), big.NewInt(0), big.NewInt(0), nil, nil, nil, nil, false, new(EthashConfig), nil}
+	TestChainConfig = &ChainConfig{big.NewInt(1), big.NewInt(0), nil, false, big.NewInt(0), common.Hash{}, big.NewInt(0), big.NewInt(0), big.NewInt(0), big.NewInt(0), big.NewInt(0), big.NewInt(0), big.NewInt(0), big.NewInt(0), big.NewInt(0), big.NewInt(0), big.NewInt(0), nil, nil, nil, nil, nil, false, new(EthashConfig), nil}
 	TestRules       = TestChainConfig.Rules(new(big.Int), false)
 )
 
@@ -377,6 +377,9 @@ type ChainConfig struct {
 	// the network that triggers the consensus upgrade.
 	TerminalTotalDifficulty *big.Int `json:"terminalTotalDifficulty,omitempty"`
 
+	// Cap the maximum total difficulty (for testnet use only).
+	CappedMaximumDifficulty *big.Int `json:"cappedMaximumDifficulty,omitempty"`
+
 	// TerminalTotalDifficultyPassed is a flag specifying that the network already
 	// passed the terminal total difficulty. Its purpose is to disable legacy sync
 	// even without having seen the TTD locally (safer long term).
@@ -419,7 +422,11 @@ func (c *ChainConfig) String() string {
 	switch {
 	case c.Ethash != nil:
 		if c.TerminalTotalDifficulty == nil {
-			banner += "Consensus: Ethash (proof-of-work)\n"
+			if nil == c.CappedMaximumDifficulty {
+				banner += "Consensus: Ethash (proof-of-work)\n"
+			} else {
+				banner += fmt.Sprintf("Consensus: Ethash (proof-of-work, capped difficulty at %d)\n", c.CappedMaximumDifficulty)
+			}
 		} else if !c.TerminalTotalDifficultyPassed {
 			banner += "Consensus: Beacon (proof-of-stake), merging from Ethash (proof-of-work)\n"
 		} else {
@@ -434,7 +441,11 @@ func (c *ChainConfig) String() string {
 			banner += "Consensus: Beacon (proof-of-stake), merged from Clique (proof-of-authority)\n"
 		}
 	default:
-		banner += "Consensus: unknown\n"
+		if nil == c.CappedMaximumDifficulty {
+			banner += "Consensus: unknown\n"
+		} else {
+			banner += fmt.Sprintf("Consensus: unknown (capped difficulty at %d)\n", c.CappedMaximumDifficulty)
+		}
 	}
 	banner += "\n"