diff --git a/eth/tools/_utils/normalization.py b/eth/tools/_utils/normalization.py
index 72f40a1e99..d70f5eedb8 100644
--- a/eth/tools/_utils/normalization.py
+++ b/eth/tools/_utils/normalization.py
@@ -542,6 +542,8 @@ def normalize_block_header(header: Dict[str, Any]) -> Dict[str, Any]:
     }
     if 'blocknumber' in header:
         normalized_header['blocknumber'] = to_int(header['blocknumber'])
+    if 'baseFeePerGas' in header:
+        normalized_header['baseFeePerGas'] = to_int(header['baseFeePerGas'])
     if 'chainname' in header:
         normalized_header['chainname'] = header['chainname']
     if 'chainnetwork' in header:
diff --git a/eth/tools/fixtures/helpers.py b/eth/tools/fixtures/helpers.py
index bbc4a8b4a7..e82700842d 100644
--- a/eth/tools/fixtures/helpers.py
+++ b/eth/tools/fixtures/helpers.py
@@ -11,7 +11,10 @@
     Type,
 )
 
-from eth_utils.toolz import first
+from eth_utils.toolz import (
+    assoc,
+    first,
+)
 
 from eth_utils import (
     to_normalized_address,
@@ -133,6 +136,10 @@ def chain_vm_configuration(fixture: Dict[str, Any]) -> Iterable[Tuple[int, Type[
         return (
             (0, BerlinVM),
         )
+    elif network == 'London':
+        return (
+            (0, LondonVM),
+        )
     elif network == 'FrontierToHomesteadAt5':
         HomesteadVM = BaseHomesteadVM.configure(support_dao_fork=False)
         return (
@@ -177,23 +184,28 @@ def genesis_fields_from_fixture(fixture: Dict[str, Any]) -> Dict[str, Any]:
     Convert all genesis fields in a fixture to a dictionary of header fields and values.
     """
 
-    return {
-        'parent_hash': fixture['genesisBlockHeader']['parentHash'],
-        'uncles_hash': fixture['genesisBlockHeader']['uncleHash'],
-        'coinbase': fixture['genesisBlockHeader']['coinbase'],
-        'state_root': fixture['genesisBlockHeader']['stateRoot'],
-        'transaction_root': fixture['genesisBlockHeader']['transactionsTrie'],
-        'receipt_root': fixture['genesisBlockHeader']['receiptTrie'],
-        'bloom': fixture['genesisBlockHeader']['bloom'],
-        'difficulty': fixture['genesisBlockHeader']['difficulty'],
-        'block_number': fixture['genesisBlockHeader']['number'],
-        'gas_limit': fixture['genesisBlockHeader']['gasLimit'],
-        'gas_used': fixture['genesisBlockHeader']['gasUsed'],
-        'timestamp': fixture['genesisBlockHeader']['timestamp'],
-        'extra_data': fixture['genesisBlockHeader']['extraData'],
-        'mix_hash': fixture['genesisBlockHeader']['mixHash'],
-        'nonce': fixture['genesisBlockHeader']['nonce'],
+    header_fields = fixture['genesisBlockHeader']
+    base_fields = {
+        'parent_hash': header_fields['parentHash'],
+        'uncles_hash': header_fields['uncleHash'],
+        'coinbase': header_fields['coinbase'],
+        'state_root': header_fields['stateRoot'],
+        'transaction_root': header_fields['transactionsTrie'],
+        'receipt_root': header_fields['receiptTrie'],
+        'bloom': header_fields['bloom'],
+        'difficulty': header_fields['difficulty'],
+        'block_number': header_fields['number'],
+        'gas_limit': header_fields['gasLimit'],
+        'gas_used': header_fields['gasUsed'],
+        'timestamp': header_fields['timestamp'],
+        'extra_data': header_fields['extraData'],
+        'mix_hash': header_fields['mixHash'],
+        'nonce': header_fields['nonce'],
     }
+    if 'baseFeePerGas' in header_fields:
+        return assoc(base_fields, 'base_fee_per_gas', header_fields['baseFeePerGas'])
+    else:
+        return base_fields
 
 
 def genesis_params_from_fixture(fixture: Dict[str, Any]) -> Dict[str, Any]:
diff --git a/eth/vm/forks/london/headers.py b/eth/vm/forks/london/headers.py
index ea99db2727..ba2eb4d144 100644
--- a/eth/vm/forks/london/headers.py
+++ b/eth/vm/forks/london/headers.py
@@ -108,17 +108,25 @@ def create_header_from_parent(difficulty_fn: Callable[[BlockHeaderAPI, int], int
                 header_params['timestamp'],
             )
 
+    # The general fill function doesn't recognize this custom field, so remove it
+    configured_fee_per_gas = header_params.pop('base_fee_per_gas', None)
+
     all_fields = fill_header_params_from_parent(parent_header, **header_params)
 
-    # must add the new field *after* filling, because the general fill function doesn't recognize it
-    base_fee_per_gas = calculate_expected_base_fee_per_gas(parent_header)
-    if 'base_fee_per_gas' in header_params and all_fields['base_fee_per_gas'] != base_fee_per_gas:
-        raise ValidationError(
-            f"Cannot select an invalid base_fee_per_gas of:"
-            f" {all_fields['base_fee_per_gas']!r}, expected: {base_fee_per_gas}"
-        )
+    calculated_fee_per_gas = calculate_expected_base_fee_per_gas(parent_header)
+    if configured_fee_per_gas is None:
+        all_fields['base_fee_per_gas'] = calculated_fee_per_gas
     else:
-        all_fields['base_fee_per_gas'] = base_fee_per_gas
+        # Must not configure an invalid base fee. So verify that either:
+        #   1. This is the genesis header, or
+        #   2. The configured value matches the calculated value from the parent
+        if parent_header is None or configured_fee_per_gas == calculated_fee_per_gas:
+            all_fields['base_fee_per_gas'] = configured_fee_per_gas
+        else:
+            raise ValidationError(
+                f"Cannot select an invalid base_fee_per_gas of:"
+                f" {configured_fee_per_gas}, expected: {calculated_fee_per_gas}"
+            )
 
     new_header = LondonBlockHeader(**all_fields)  # type:ignore
     return new_header
diff --git a/newsfragments/2022.internal.rst b/newsfragments/2022.internal.rst
new file mode 100644
index 0000000000..1c0726fbfc
--- /dev/null
+++ b/newsfragments/2022.internal.rst
@@ -0,0 +1 @@
+During fixture tests, verify that the generated genesis block matches the fixture's RLP-encoding.
diff --git a/tests/json-fixtures/blockchain/test_blockchain.py b/tests/json-fixtures/blockchain/test_blockchain.py
index 150a5a77c2..0162611ffc 100644
--- a/tests/json-fixtures/blockchain/test_blockchain.py
+++ b/tests/json-fixtures/blockchain/test_blockchain.py
@@ -10,6 +10,7 @@
 
 from eth.tools.rlp import (
     assert_mined_block_unchanged,
+    assert_headers_eq,
 )
 from eth.tools._utils.normalization import (
     normalize_blockchain_fixtures,
@@ -24,6 +25,7 @@
     should_run_slow_tests,
     verify_state,
 )
+from eth.vm.header import HeaderSedes
 
 
 ROOT_PROJECT_DIR = Path(__file__).parents[3]
@@ -325,15 +327,22 @@ def test_blockchain_fixtures(fixture_data, fixture):
     except ValueError as e:
         raise AssertionError(f"could not load chain for {fixture_data}") from e
 
-    # TODO: find out if this is supposed to pass?
-    # if 'genesisRLP' in fixture:
-    #     assert rlp.encode(genesis_header) == fixture['genesisRLP']
-
     genesis_fields = genesis_fields_from_fixture(fixture)
 
     genesis_block = chain.get_canonical_block_by_number(0)
     genesis_header = genesis_block.header
 
+    # Validate the genesis header RLP against the generated header
+    if 'genesisRLP' in fixture:
+        # Super hacky, but better than nothing: extract the header, then re-decode it
+        fixture_decoded_block = rlp.decode(fixture['genesisRLP'])
+        fixture_encoded_header = rlp.encode(fixture_decoded_block[0])
+        fixture_header = rlp.decode(fixture_encoded_header, sedes=HeaderSedes)
+        # Error message with pretty output if header doesn't match
+        assert_headers_eq(fixture_header, genesis_header)
+        # Last gut check that transactions & receipts are valid, too
+        assert rlp.encode(genesis_block) == fixture['genesisRLP']
+
     assert_imported_genesis_header_unchanged(genesis_fields, genesis_header)
 
     # 1 - mine the genesis block