diff --git a/setup.py b/setup.py
index 801f215d0..3a4fd1e18 100644
--- a/setup.py
+++ b/setup.py
@@ -96,7 +96,7 @@ from lru import LRU
 
 from eth2spec.utils.ssz.ssz_impl import hash_tree_root, copy
 from eth2spec.utils.ssz.ssz_typing import (
-    View, boolean, Container, List, Vector, uint64,
+    View, boolean, Container, List, Vector, uint64, uint8,
     Bytes1, Bytes4, Bytes32, Bytes48, Bytes96, Bitlist, Bitvector,
 )
 from eth2spec.utils import bls
diff --git a/specs/phase0/beacon-chain.md b/specs/phase0/beacon-chain.md
index df9390964..c7dd25d3a 100644
--- a/specs/phase0/beacon-chain.md
+++ b/specs/phase0/beacon-chain.md
@@ -737,7 +737,7 @@ def compute_shuffled_index(index: uint64, index_count: uint64, seed: Bytes32) ->
         flip = (pivot + index_count - index) % index_count
         position = max(index, flip)
         source = hash(seed + int_to_bytes(current_round, length=1) + int_to_bytes(position // 256, length=4))
-        byte = source[(position % 256) // 8]
+        byte = uint8(source[(position % 256) // 8])
         bit = (byte >> (position % 8)) % 2
         index = flip if bit else index
 
@@ -1317,7 +1317,7 @@ def process_justification_and_finalization(state: BeaconState) -> None:
 
     # Process justifications
     state.previous_justified_checkpoint = state.current_justified_checkpoint
-    state.justification_bits[1:] = state.justification_bits[:-1]
+    state.justification_bits[1:] = state.justification_bits[:JUSTIFICATION_BITS_LENGTH - 1]
     state.justification_bits[0] = 0b0
     matching_target_attestations = get_matching_target_attestations(state, previous_epoch)  # Previous epoch
     if get_attesting_balance(state, matching_target_attestations) * 3 >= get_total_active_balance(state) * 2:
diff --git a/tests/core/pyspec/eth2spec/test/phase0/epoch_processing/test_process_rewards_and_penalties.py b/tests/core/pyspec/eth2spec/test/phase0/epoch_processing/test_process_rewards_and_penalties.py
index d3744f897..72bdd3e92 100644
--- a/tests/core/pyspec/eth2spec/test/phase0/epoch_processing/test_process_rewards_and_penalties.py
+++ b/tests/core/pyspec/eth2spec/test/phase0/epoch_processing/test_process_rewards_and_penalties.py
@@ -48,7 +48,7 @@ def test_genesis_epoch_full_attestations_no_rewards(spec, state):
             attestation = get_valid_attestation(spec, state, signed=True)
             attestations.append(attestation)
         # fill each created slot in state after inclusion delay
-        if slot - spec.MIN_ATTESTATION_INCLUSION_DELAY >= 0:
+        if slot >= spec.MIN_ATTESTATION_INCLUSION_DELAY:
             include_att = attestations[slot - spec.MIN_ATTESTATION_INCLUSION_DELAY]
             add_attestations_to_state(spec, state, [include_att], state.slot)
         next_slot(spec, state)