diff --git a/params/config.go b/params/config.go
index e89fb17a1..80fe3cdd8 100644
--- a/params/config.go
+++ b/params/config.go
@@ -708,8 +708,8 @@ func (c *ChainConfig) checkCompatible(newcfg *ChainConfig, headNumber *big.Int,
 	if isForkBlockIncompatible(c.EIP158Block, newcfg.EIP158Block, headNumber) {
 		return newBlockCompatError("EIP158 fork block", c.EIP158Block, newcfg.EIP158Block)
 	}
-	// allow mismatching ChainID if we're at the PrimordialPulseBlock
-	if c.IsEIP158(headNumber) && !configBlockEqual(c.ChainID, newcfg.ChainID) && !newcfg.IsPrimordialPulseBlock(new(big.Int).Add(headNumber, common.Big1)) {
+	// allow mismatching ChainID if there is a PrimordialPulse block ahead
+	if c.IsEIP158(headNumber) && !configBlockEqual(c.ChainID, newcfg.ChainID) && !newcfg.PrimordialPulseAhead(headNumber) {
 		return newBlockCompatError("EIP158 chain ID", c.EIP158Block, newcfg.EIP158Block)
 	}
 	if isForkBlockIncompatible(c.ByzantiumBlock, newcfg.ByzantiumBlock, headNumber) {