diff --git a/eth/precompiles/modexp.py b/eth/precompiles/modexp.py
index f971bd4b93..e477ce6013 100644
--- a/eth/precompiles/modexp.py
+++ b/eth/precompiles/modexp.py
@@ -35,7 +35,7 @@ def _compute_complexity(length):
             length ** 2 // 4 + 96 * length - 3072
         )
     else:
-        return 2 ** 2 // 16 + 480 * length - 199680
+        return length ** 2 // 16 + 480 * length - 199680
 
 
 def _extract_lengths(data):
diff --git a/fixtures b/fixtures
index 47b09f42c0..f4faae91c5 160000
--- a/fixtures
+++ b/fixtures
@@ -1 +1 @@
-Subproject commit 47b09f42c0681548a00da5ab1c98808b368af49a
+Subproject commit f4faae91c5ba192c3fd9b8cf418c24e627786312
diff --git a/tests/core/vm/test_modexp_precompile.py b/tests/core/vm/test_modexp_precompile.py
index 1a2210981b..3d8f32af65 100644
--- a/tests/core/vm/test_modexp_precompile.py
+++ b/tests/core/vm/test_modexp_precompile.py
@@ -41,11 +41,11 @@
         (EIP198_VECTOR_A, 13056),
         (
             EIP198_VECTOR_C,
-            708647586132375115992254428253169996062012306153720251921480414128428353393856280,
+            10684346944173007063723051170445283632835119638284563472873463025465780712173320789629146724657549280936306536701227228889744512638312451529980055895215896,  # noqa: E501
         ),
     ),
 )
-def test_modexp_gas_fee_calcultation(data, expected):
+def test_modexp_gas_fee_calculation(data, expected):
     actual = _compute_modexp_gas_fee(data)
     assert actual == expected
 
diff --git a/tests/json-fixtures/test_blockchain.py b/tests/json-fixtures/test_blockchain.py
index 5d0de5382a..ce72ba1ca7 100644
--- a/tests/json-fixtures/test_blockchain.py
+++ b/tests/json-fixtures/test_blockchain.py
@@ -32,17 +32,33 @@
 BASE_FIXTURE_PATH = os.path.join(ROOT_PROJECT_DIR, 'fixtures', 'BlockchainTests')
 
 
+# These are tests that are thought to be incorrect or buggy upstream,
+# at the commit currently checked out in submodule `fixtures`.
+# Ideally, this list should be empty.
+# WHEN ADDING ENTRIES, ALWAYS PROVIDE AN EXPLANATION!
+INCORRECT_UPSTREAM_TESTS = {
+    # The test considers a "synthetic" scenario (the state described there can't
+    # be arrived at using regular consensus rules).
+    # * https://github.com/ethereum/py-evm/pull/1224#issuecomment-418775512
+    # The result is in conflict with the yellow-paper:
+    # * https://github.com/ethereum/py-evm/pull/1224#issuecomment-418800369
+    ('GeneralStateTests/stRevertTest/RevertInCreateInInit_d0g0v0.json', 'RevertInCreateInInit_d0g0v0_Byzantium'),  # noqa: E501
+}
+
+
 def blockchain_fixture_mark_fn(fixture_path, fixture_name):
     if fixture_path.startswith('bcExploitTest'):
         return pytest.mark.skip("Exploit tests are slow")
     elif fixture_path == 'bcWalletTest/walletReorganizeOwners.json':
         return pytest.mark.skip("Wallet owner reorganization tests are slow")
+    elif (fixture_path, fixture_name) in INCORRECT_UPSTREAM_TESTS:
+        return pytest.mark.xfail(reason="Listed in INCORRECT_UPSTREAM_TESTS.")
 
 
 def blockchain_fixture_ignore_fn(fixture_path, fixture_name):
     if fixture_path.startswith('GeneralStateTests'):
         # General state tests are also exported as blockchain tests.  We
-        # skip them here so we don't run them twice"
+        # skip them here so we don't run them twice
         return True
 
 
diff --git a/tests/json-fixtures/test_state.py b/tests/json-fixtures/test_state.py
index d35597e176..91b0ab468e 100644
--- a/tests/json-fixtures/test_state.py
+++ b/tests/json-fixtures/test_state.py
@@ -133,6 +133,20 @@ def expand_fixtures_forks(all_fixtures):
 }
 
 
+# These are tests that are thought to be incorrect or buggy upstream,
+# at the commit currently checked out in submodule `fixtures`.
+# Ideally, this list should be empty.
+# WHEN ADDING ENTRIES, ALWAYS PROVIDE AN EXPLANATION!
+INCORRECT_UPSTREAM_TESTS = {
+    # The test considers a "synthetic" scenario (the state described there can't
+    # be arrived at using regular consensus rules).
+    # * https://github.com/ethereum/py-evm/pull/1224#issuecomment-418775512
+    # The result is in conflict with the yellow-paper:
+    # * https://github.com/ethereum/py-evm/pull/1224#issuecomment-418800369
+    ('stRevertTest/RevertInCreateInInit.json', 'RevertInCreateInInit', 'Byzantium', 0),
+}
+
+
 def mark_statetest_fixtures(fixture_path, fixture_key, fixture_fork, fixture_index):
     fixture_id = (fixture_path, fixture_key, fixture_fork, fixture_index)
     if fixture_path.startswith('stTransactionTest/zeroSigTransa'):
@@ -144,6 +158,8 @@ def mark_statetest_fixtures(fixture_path, fixture_key, fixture_fork, fixture_ind
             return pytest.mark.skip("Skipping slow test")
     elif fixture_path.startswith('stQuadraticComplexityTest'):
         return pytest.mark.skip("Skipping slow test")
+    elif fixture_id in INCORRECT_UPSTREAM_TESTS:
+        return pytest.mark.xfail(reason="Listed in INCORRECT_UPSTREAM_TESTS.")
 
 
 def pytest_generate_tests(metafunc):
diff --git a/tests/trinity/json-fixtures-over-rpc/test_rpc_fixtures.py b/tests/trinity/json-fixtures-over-rpc/test_rpc_fixtures.py
index f65dbed88c..297a82b270 100644
--- a/tests/trinity/json-fixtures-over-rpc/test_rpc_fixtures.py
+++ b/tests/trinity/json-fixtures-over-rpc/test_rpc_fixtures.py
@@ -92,6 +92,19 @@
     'DelegateCallSpam_EIP150',
 )
 
+# These are tests that are thought to be incorrect or buggy upstream,
+# at the commit currently checked out in submodule `fixtures`.
+# Ideally, this list should be empty.
+# WHEN ADDING ENTRIES, ALWAYS PROVIDE AN EXPLANATION!
+INCORRECT_UPSTREAM_TESTS = {
+    # The test considers a "synthetic" scenario (the state described there can't
+    # be arrived at using regular consensus rules).
+    # * https://github.com/ethereum/py-evm/pull/1224#issuecomment-418775512
+    # The result is in conflict with the yellow-paper:
+    # * https://github.com/ethereum/py-evm/pull/1224#issuecomment-418800369
+    ('GeneralStateTests/stRevertTest/RevertInCreateInInit_d0g0v0.json', 'RevertInCreateInInit_d0g0v0_Byzantium'),  # noqa: E501
+}
+
 RPC_STATE_NORMALIZERS = {
     'balance': remove_leading_zeros,
     'code': empty_to_0x,
@@ -162,6 +175,8 @@ def blockchain_fixture_mark_fn(fixture_path, fixture_name):
             if not should_run_slow_tests():
                 return pytest.mark.skip("skipping slow test on a quick run")
             break
+    if (fixture_path, fixture_name) in INCORRECT_UPSTREAM_TESTS:
+        return pytest.mark.xfail(reason="Listed in INCORRECT_UPSTREAM_TESTS.")
 
 
 def pytest_generate_tests(metafunc):