diff --git a/stateless/test_block_witness.nim b/stateless/test_block_witness.nim
index 4ef23a431..b1422f7d8 100644
--- a/stateless/test_block_witness.nim
+++ b/stateless/test_block_witness.nim
@@ -40,7 +40,7 @@ proc testGetBranch(tester: Tester, rootHash: KeccakHash, testStatusIMPL: var Tes
       else:
         var tb = initTreeBuilder(witness, db, flags)
 
-      var root = tb.treeNode()
+      var root = tb.buildTree()
       check root.data == rootHash.data
   except ContractCodeError as e:
     debugEcho "CONTRACT CODE ERROR: ", e.msg
diff --git a/stateless/test_witness_keys.nim b/stateless/test_witness_keys.nim
index 16aec21d4..292a69e6e 100644
--- a/stateless/test_witness_keys.nim
+++ b/stateless/test_witness_keys.nim
@@ -67,7 +67,7 @@ proc runTest(numPairs: int) =
     var tb = initTreeBuilder(input, db, {wfEIP170})
   else:
     var tb = initTreeBuilder(witness, db, {wfEIP170})
-  var root = tb.treeNode()
+  var root = tb.buildTree()
   debugEcho "root: ", root.data.toHex
   debugEcho "rootHash: ", rootHash.data.toHex
   doAssert root.data == rootHash.data
diff --git a/stateless/tree_from_witness.nim b/stateless/tree_from_witness.nim
index bbc27eb37..5d0b8c5e6 100644
--- a/stateless/tree_from_witness.nim
+++ b/stateless/tree_from_witness.nim
@@ -60,6 +60,8 @@ when defined(useInputStream):
   template read(t: var TreeBuilder, len: int): auto =
     t.input.read(len)
 
+  template readable(t: var TreeBuilder): bool =
+    t.input.readable
 else:
   template readByte(t: var TreeBuilder): byte =
     let pos = t.pos
@@ -69,9 +71,8 @@ else:
   template len(t: TreeBuilder): int =
     t.input.len
 
-  template peek(t: TreeBuilder): byte =
-    t.input.peek
-    t.input[t.pos]
+  template readable(t: var TreeBuilder): bool =
+    t.pos < t.input.len
 
   template read(t: var TreeBuilder, len: int): auto =
     let pos = t.pos
@@ -115,8 +116,43 @@ proc extensionNode(t: var TreeBuilder, depth: int, storageMode: bool): NodeKey
 proc accountNode(t: var TreeBuilder, depth: int): NodeKey
 proc accountStorageLeafNode(t: var TreeBuilder, depth: int): NodeKey
 proc hashNode(t: var TreeBuilder): NodeKey
+proc treeNode(t: var TreeBuilder, depth: int = 0, storageMode = false): NodeKey
 
-proc treeNode*(t: var TreeBuilder, depth: int = 0, storageMode = false): NodeKey =
+proc buildTree*(t: var TreeBuilder): KeccakHash =
+  let version = t.readByte().int
+  if version != BlockWitnessVersion.int:
+    raise newException(ParsingError, "Wrong block witness version")
+
+  # one or more trees
+
+  # we only parse one tree here
+  let metadataType = t.readByte().int
+  if metadataType != MetadataNothing.int:
+    raise newException(ParsingError, "This tree builder support no metadata")
+
+  var res = treeNode(t)
+  if res.usedBytes != 32:
+    raise newException(ParsingError, "Buildtree should produce hash")
+
+  result.data = res.data
+
+proc buildForest*(t: var TreeBuilder): seq[KeccakHash] =
+  let version = t.readByte().int
+  if version != BlockWitnessVersion.int:
+    raise newException(ParsingError, "Wrong block witness version")
+
+  while t.readable:
+    let metadataType = t.readByte().int
+    if metadataType != MetadataNothing.int:
+      raise newException(ParsingError, "This tree builder support no metadata")
+
+    var res = treeNode(t)
+    if res.usedBytes != 32:
+      raise newException(ParsingError, "Buildtree should produce hash")
+
+    result.add KeccakHash(data: res.data)
+
+proc treeNode(t: var TreeBuilder, depth: int = 0, storageMode = false): NodeKey =
   assert(depth < 64)
   let nodeType = TrieNodeType(t.readByte)
 
diff --git a/stateless/witness_from_tree.nim b/stateless/witness_from_tree.nim
index 637e927c0..f178162ef 100644
--- a/stateless/witness_from_tree.nim
+++ b/stateless/witness_from_tree.nim
@@ -244,8 +244,17 @@ proc getBranchRecurseAux(wb: var WitnessBuilder, node: openArray[byte], path: Ni
     raise newException(CorruptedTrieDatabase,
                        "HexaryTrie node with an unexpected number of children")
 
-proc buildWitness*(wb: var WitnessBuilder; address: EthAddress): seq[byte] =
+proc buildWitness*(wb: var WitnessBuilder; address: EthAddress, withVersion: bool = true): seq[byte] =
+  # witness version
+  wb.output.append(BlockWitnessVersion.byte)
+
+  # one or more trees
+
+  # we only output one tree
+  wb.output.append(MetadataNothing.byte)
   let key = keccak(address)
   var node = wb.db.get(wb.root.data)
   getBranchRecurseAux(wb, node, initNibbleRange(key.data), 0, false)
+
+  # result
   result = wb.output.getOutput(seq[byte])
diff --git a/stateless/witness_types.nim b/stateless/witness_types.nim
index 5dbd6ee41..dd1c8f9d5 100644
--- a/stateless/witness_types.nim
+++ b/stateless/witness_types.nim
@@ -15,9 +15,14 @@ type
     wfNoFlag
     wfEIP170 # fork >= Spurious Dragon
 
+  MetadataType* = enum
+    MetadataNothing
+    MetadataSomething
+
   WitnessFlags* = set[WitnessFlag]
 
   ContractCodeError* = object of ValueError
+  ParsingError* = object of ValueError
 
 const
   StorageLeafNodeType* = AccountNodeType
@@ -33,6 +38,5 @@ func branchMaskBitIsSet*(x: uint, i: int): bool {.inline.} =
 
 func constructBranchMask*(b1, b2: byte): uint {.inline.} =
   result = uint(b1) shl 8 or uint(b2)
-  if countOnes(result) < 2:
-    debugEcho "MASK: ", result
-  assert(countOnes(result) > 1)
+  if countOnes(result) < 2 or ((result and (not 0x1FFFF'u)) != 0):
+    raise newException(ParsingError, "Invalid branch mask pattern")