diff --git a/core/vm/contracts.go b/core/vm/contracts.go
index a1ea48fa00ef..42cff82bbd05 100644
--- a/core/vm/contracts.go
+++ b/core/vm/contracts.go
@@ -29,6 +29,7 @@ import (
 	"github.com/XinFinOrg/XDPoSChain/crypto/blake2b"
 	"github.com/XinFinOrg/XDPoSChain/crypto/bn256"
 	"github.com/XinFinOrg/XDPoSChain/params"
+	big2 "github.com/holiman/big"
 
 	//lint:ignore SA1019 Needed for precompile
 	"golang.org/x/crypto/ripemd160"
@@ -401,17 +402,17 @@ func (c *bigModExp) Run(input []byte) ([]byte, error) {
 	}
 	// Retrieve the operands and execute the exponentiation
 	var (
-		base = new(big.Int).SetBytes(getData(input, 0, baseLen))
-		exp  = new(big.Int).SetBytes(getData(input, baseLen, expLen))
-		mod  = new(big.Int).SetBytes(getData(input, baseLen+expLen, modLen))
+		base = new(big2.Int).SetBytes(getData(input, 0, baseLen))
+		exp  = new(big2.Int).SetBytes(getData(input, baseLen, expLen))
+		mod  = new(big2.Int).SetBytes(getData(input, baseLen+expLen, modLen))
 		v    []byte
 	)
 	switch {
 	case mod.BitLen() == 0:
 		// Modulo 0 is undefined, return zero
 		return common.LeftPadBytes([]byte{}, int(modLen)), nil
-	case base.Cmp(common.Big1) == 0:
-		//If base == 1, then we can just return base % mod (if mod >= 1, which it is)
+	case base.BitLen() == 1: // a bit length of 1 means it's 1 (or -1).
+		// If base == 1, then we can just return base % mod (if mod >= 1, which it is)
 		v = base.Mod(base, mod).Bytes()
 	default:
 		v = base.Exp(base, exp, mod).Bytes()