diff --git a/test_libs/pyspec/eth2spec/utils/bls_stub.py b/test_libs/pyspec/eth2spec/utils/bls_stub.py
index 108c4ef71..ae97de175 100644
--- a/test_libs/pyspec/eth2spec/utils/bls_stub.py
+++ b/test_libs/pyspec/eth2spec/utils/bls_stub.py
@@ -9,4 +9,4 @@ def bls_verify_multiple(pubkeys, message_hashes, signature, domain):
 
 
 def bls_aggregate_pubkeys(pubkeys):
-    return b'\x42' * 96
+    return b'\x42' * 48
diff --git a/test_libs/pyspec/tests/block_processing/test_process_attestation.py b/test_libs/pyspec/tests/block_processing/test_process_attestation.py
index 708d68dca..6851561e9 100644
--- a/test_libs/pyspec/tests/block_processing/test_process_attestation.py
+++ b/test_libs/pyspec/tests/block_processing/test_process_attestation.py
@@ -124,7 +124,7 @@ def test_bad_previous_crosslink(state):
     for _ in range(spec.MIN_ATTESTATION_INCLUSION_DELAY):
         next_slot(state)
 
-    state.current_crosslinks[attestation.data.crosslink.shard].epoch += 10
+    state.current_crosslinks[attestation.data.crosslink.shard].end_epoch += 10
 
     pre_state, post_state = run_attestation_processing(state, attestation, False)
 
diff --git a/test_libs/pyspec/tests/helpers.py b/test_libs/pyspec/tests/helpers.py
index 5ddb2dc15..7af210f85 100644
--- a/test_libs/pyspec/tests/helpers.py
+++ b/test_libs/pyspec/tests/helpers.py
@@ -177,6 +177,7 @@ def build_attestation_data(state, slot, shard):
         justified_block_root = state.current_justified_root
 
     crosslinks = state.current_crosslinks if slot_to_epoch(slot) == get_current_epoch(state) else state.previous_crosslinks
+    parent_crosslink = crosslinks[shard]
     return AttestationData(
         beacon_block_root=block_root,
         source_epoch=justified_epoch,
@@ -185,9 +186,10 @@ def build_attestation_data(state, slot, shard):
         target_root=epoch_boundary_root,
         crosslink=Crosslink(
             shard=shard,
-            epoch=min(slot_to_epoch(slot), crosslinks[shard].epoch + MAX_EPOCHS_PER_CROSSLINK),
+            start_epoch=parent_crosslink.end_epoch,
+            end_epoch=min(slot_to_epoch(slot), parent_crosslink.end_epoch + MAX_EPOCHS_PER_CROSSLINK),
             data_root=spec.ZERO_HASH,
-            parent_root=hash_tree_root(crosslinks[shard]),
+            parent_root=hash_tree_root(parent_crosslink),
         ),
     )