diff --git a/ethcore/res/ethereum/frontier.json b/ethcore/res/ethereum/frontier.json
index 4f0a836ff..33f0b833c 100644
--- a/ethcore/res/ethereum/frontier.json
+++ b/ethcore/res/ethereum/frontier.json
@@ -3,7 +3,7 @@
 	"engineName": "Ethash",
 	"params": {
 		"accountStartNonce": "0x00",
-		"frontierCompatibilityModeLimit": "0xf4240",
+		"frontierCompatibilityModeLimit": "0xf4240fff",
 		"maximumExtraDataSize": "0x20",
 		"tieBreakingGas": false,
 		"minGasLimit": "0x1388",
diff --git a/ethcore/res/ethereum/frontier_like_test.json b/ethcore/res/ethereum/frontier_like_test.json
index 84a6200fd..7ab6a58f4 100644
--- a/ethcore/res/ethereum/frontier_like_test.json
+++ b/ethcore/res/ethereum/frontier_like_test.json
@@ -3,7 +3,7 @@
 	"engineName": "Ethash",
 	"params": {
 		"accountStartNonce": "0x00",
-		"frontierCompatibilityModeLimit": "0xf4240",
+		"frontierCompatibilityModeLimit": "0xf4240fff",
 		"maximumExtraDataSize": "0x20",
 		"tieBreakingGas": false,
 		"minGasLimit": "0x1388",