diff --git a/premix/parser.nim b/premix/parser.nim
index aad83678a..4c489de14 100644
--- a/premix/parser.nim
+++ b/premix/parser.nim
@@ -53,11 +53,6 @@ proc fromJson*(n: JsonNode, name: string, x: var Blob) =
 
 proc fromJson*(n: JsonNode, name: string, x: var UInt256) =
   x = UInt256.fromHex(n[name].getStr())
-  if x.prefixHex != toLowerAscii(n[name].getStr()):
-    debugEcho "name: ", name
-    debugEcho "A: ", x.prefixHex
-    debugEcho "B: ", toLowerAscii(n[name].getStr())
-    quit(1)
   doAssert(x.prefixHex == toLowerAscii(n[name].getStr()), name)
 
 proc fromJson*(n: JsonNode, name: string, x: var SomeInteger) =
diff --git a/tests/test_blockchain_json.nim b/tests/test_blockchain_json.nim
index ea48f9199..6e01709cd 100644
--- a/tests/test_blockchain_json.nim
+++ b/tests/test_blockchain_json.nim
@@ -72,11 +72,14 @@ func normalizeNumber(n: JsonNode): JsonNode =
   let str = n.getStr
   # paranoid checks
   doAssert n.kind == Jstring
-  doAssert str.len > 3
   doAssert str[0] == '0' and str[1] == 'x'
   # real normalization
   # strip leading 0
-  if str == "0x00":
+  if str == "0x":
+    result = newJString("0x0")
+  elif str == "0x0":
+    result = n
+  elif str == "0x00":
     result = newJString("0x0")
   elif str[2] == '0':
     var i =  2
@@ -197,6 +200,7 @@ func vmConfiguration(network: string): VMConfig =
   of "HomesteadToEIP150At5": result = [(0, FkHomestead), (5, FkTangerine)]
   of "FrontierToHomesteadAt5": result = [(0, FkFrontier), (5, FkHomestead)]
   of "ByzantiumToConstantinopleFixAt5": result = [(0, FkByzantium), (5, FkConstantinople)]
+  of "Istanbul": result = [(0, FkIstanbul), (0, FkIstanbul)]
   else:
     raise newException(ValueError, "unsupported network")
 
@@ -279,7 +283,7 @@ proc processBlock(vmState: BaseVMState, minedBlock: PlainBlock, fork: Fork) =
     vmState.receipts[txIndex] = makeReceipt(vmState, fork)
 
   if vmState.cumulativeGasUsed != minedBlock.header.gasUsed:
-    raise newException(ValidationError, "wrong gas used in header")
+    raise newException(ValidationError, &"wrong gas used in header expected={minedBlock.header.gasUsed}, actual={vmState.cumulativeGasUsed}")
 
   assignBlockRewards(minedBlock, vmState, fork, vmState.chainDB)
 
@@ -663,6 +667,8 @@ proc main() =
     # run all test fixtures
     suite "block chain json tests":
       jsonTest("BlockchainTests", testFixture)
+    suite "new block chain json tests":
+      jsonTest("NewBlockchainTests", testFixture)
   else:
     # execute single test in debug mode
     let config = getConfiguration()
@@ -670,7 +676,7 @@ proc main() =
       echo "missing test subject"
       quit(QuitFailure)
 
-    let path = "tests" / "fixtures" / "BlockChainTests"
+    let path = "tests" / "fixtures" / "NewBlockChainTests"
     let n = json.parseFile(path / config.testSubject)
     var testStatusIMPL: TestStatus
     testFixture(n, testStatusIMPL, debugMode = true, config.trace)
diff --git a/tests/test_generalstate_json.nim b/tests/test_generalstate_json.nim
index aa001a924..01bab8c63 100644
--- a/tests/test_generalstate_json.nim
+++ b/tests/test_generalstate_json.nim
@@ -176,6 +176,8 @@ proc generalStateJsonMain*(debugMode = false) =
     # run all test fixtures
     suite "generalstate json tests":
       jsonTest("GeneralStateTests", testFixture)
+    suite "new generalstate json tests":
+      jsonTest("NewGeneralStateTests", testFixture)
   else:
     # execute single test in debug mode
     let config = getConfiguration()
diff --git a/tests/test_helpers.nim b/tests/test_helpers.nim
index a5eb09613..5ea12604d 100644
--- a/tests/test_helpers.nim
+++ b/tests/test_helpers.nim
@@ -26,10 +26,18 @@ const
     FkTangerine: "EIP150",
     FkSpurious: "EIP158",
     FkByzantium: "Byzantium",
-    FkConstantinople: "ConstantinopleFix"
+    FkConstantinople: "ConstantinopleFix",
+    FkIstanbul: "Istanbul"
   }.toTable
 
-  supportedForks* = {FkFrontier, FkHomestead, FkTangerine, FkSpurious, FkByzantium, FkConstantinople}
+  supportedForks* = {
+    FkFrontier,
+    FkHomestead,
+    FkTangerine,
+    FkSpurious,
+    FkByzantium,
+    FkConstantinople,
+    FkIstanbul}
 
   nameToFork* = revmap(forkNames)