diff --git a/core/chain_util.go b/core/chain_util.go
index 7e99c7d4c1..3078fcc1df 100644
--- a/core/chain_util.go
+++ b/core/chain_util.go
@@ -41,7 +41,7 @@ var (
 func CalcDifficulty(time, parentTime uint64, parentNumber, parentDiff *big.Int) *big.Int {
 	diff := new(big.Int)
 
-	if parentNumber <= 23000 {
+	if parentNumber <= params.HardFork1 {
 	    adjust := new(big.Int).Div(parentDiff, params.DifficultyBoundDivisor)
 	} else {
 	    adjust := new(big.Int).Div(parentDiff, params.DifficultyBoundDivisor2)
diff --git a/params/protocol_params.go b/params/protocol_params.go
index ca4a2001c7..e3b89f22b1 100755
--- a/params/protocol_params.go
+++ b/params/protocol_params.go
@@ -31,6 +31,7 @@ var (
 	TxDataZeroGas          = big.NewInt(4)      // Per byte of data attached to a transaction that equals zero. NOTE: Not payable on data of calls between transactions.
 	DifficultyBoundDivisor = big.NewInt(2048)   // The bound divisor of the difficulty, used in the update calculations.
 	DifficultyBoundDivisor2 = big.NewInt(512)   // Difficulty should adjust faster.
+	HardFork1               = big.NewInt(23000) // fork at this block number
 	QuadCoeffDiv           = big.NewInt(512)    // Divisor for the quadratic particle of the memory cost equation.
 	GenesisDifficulty      = big.NewInt(131072) // Difficulty of the Genesis block.
 	DurationLimit          = big.NewInt(60)     // The decision boundary on the blocktime duration used to determine whether difficulty should go up or not.