diff --git a/res/ethereum/frontier.json b/res/ethereum/frontier.json
index 6394a9010..75a0e0bc3 100644
--- a/res/ethereum/frontier.json
+++ b/res/ethereum/frontier.json
@@ -3,7 +3,7 @@
 	"engineName": "Ethash",
 	"params": {
 		"accountStartNonce": "0x00",
-		"frontierCompatibilityModeLimit": "0xfffa2990",
+		"frontierCompatibilityModeLimit": "0xf4240",
 		"maximumExtraDataSize": "0x20",
 		"tieBreakingGas": false,
 		"minGasLimit": "0x1388",
diff --git a/res/ethereum/homestead_test.json b/res/ethereum/homestead_test.json
index ee73d0ed3..b11ef9740 100644
--- a/res/ethereum/homestead_test.json
+++ b/res/ethereum/homestead_test.json
@@ -3,7 +3,7 @@
 	"engineName": "Ethash",
 	"params": {
 		"accountStartNonce": "0x00",
-		"frontierCompatibilityModeLimit": "0xffffffff",
+		"frontierCompatibilityModeLimit": "0",
 		"maximumExtraDataSize": "0x20",
 		"minGasLimit": "0x1388",
 		"tieBreakingGas": false,
diff --git a/res/ethereum/morden.json b/res/ethereum/morden.json
index 79f9f3d99..6897b7fcb 100644
--- a/res/ethereum/morden.json
+++ b/res/ethereum/morden.json
@@ -3,7 +3,7 @@
 	"engineName": "Ethash",
 	"params": {
 		"accountStartNonce": "0x0100000",
-		"frontierCompatibilityModeLimit": "0xfffa2990",
+		"frontierCompatibilityModeLimit": "0xf4240",
 		"maximumExtraDataSize": "0x20",
 		"tieBreakingGas": false,
 		"minGasLimit": "0x1388",
diff --git a/res/ethereum/olympic.json b/res/ethereum/olympic.json
index 4318d9230..b3dfc1ed8 100644
--- a/res/ethereum/olympic.json
+++ b/res/ethereum/olympic.json
@@ -3,7 +3,7 @@
 	"engineName": "Ethash",
 	"params": {
 		"accountStartNonce": "0x00",
-		"frontierCompatibilityModeLimit": "0xffffffff",
+		"frontierCompatibilityModeLimit": "0xffffffffffffffff",
 		"maximumExtraDataSize": "0x0400",
 		"tieBreakingGas": false,
 		"minGasLimit": "125000",
diff --git a/src/ethereum/ethash.rs b/src/ethereum/ethash.rs
index 95cc1ed8b..750b8297c 100644
--- a/src/ethereum/ethash.rs
+++ b/src/ethereum/ethash.rs
@@ -132,6 +132,7 @@ impl Ethash {
 		let difficulty_bound_divisor = self.u256_param("difficultyBoundDivisor");
 		let duration_limit = self.u64_param("durationLimit");
 		let frontier_limit = self.u64_param("frontierCompatibilityModeLimit");
+		info!("Frontier limit: {}", frontier_limit);
 		let mut target = if header.number < frontier_limit {
 			if header.timestamp >= parent.timestamp + duration_limit {
 				parent.difficulty - (parent.difficulty / difficulty_bound_divisor)