diff --git a/eth2/beacon/state_machines/forks/serenity/block_validation.py b/eth2/beacon/state_machines/forks/serenity/block_validation.py
index 6cd18fc51b..9e62c965e2 100644
--- a/eth2/beacon/state_machines/forks/serenity/block_validation.py
+++ b/eth2/beacon/state_machines/forks/serenity/block_validation.py
@@ -320,7 +320,7 @@ def validate_attestation_justified_epoch(attestation_data: AttestationData,
     Validate ``justified_epoch`` field of ``attestation_data``.
     Raise ``ValidationError`` if it's invalid.
     """
-    if attestation_data.slot >= get_epoch_start_slot(current_epoch, slots_per_epoch):
+    if slot_to_epoch(attestation_data.slot + 1, slots_per_epoch) >= current_epoch:
         if attestation_data.justified_epoch != justified_epoch:
             raise ValidationError(
                 "Attestation ``slot`` is after recent epoch transition but attestation"
diff --git a/tests/eth2/beacon/state_machines/forks/test_serenity_block_attestation_validation.py b/tests/eth2/beacon/state_machines/forks/test_serenity_block_attestation_validation.py
index 7ad86003f2..0362b29a43 100644
--- a/tests/eth2/beacon/state_machines/forks/test_serenity_block_attestation_validation.py
+++ b/tests/eth2/beacon/state_machines/forks/test_serenity_block_attestation_validation.py
@@ -90,13 +90,12 @@ def test_validate_attestation_slot(sample_attestation_data_params,
         'is_valid,'
     ),
     [
-        (13, 1, 2, 0, 1, 5, True),
-        (13, 0, 2, 0, 1, 5, False),  # targeting previous_justified_epoch, should be targeting justified_epoch # noqa: E501
-        (13, 4, 2, 0, 1, 5, False),  # targeting future epoch, should be targeting justified_epoch
-        (29, 1, 3, 1, 2, 10, True),
-        (29, 2, 3, 1, 2, 10, False),  # targeting justified_epoch, should be targeting previous_justified_epoch # noqa: E501
-        (29, 3, 3, 1, 2, 10, False),  # targeting future epoch, should be targeting previous_justified_epoch # noqa: E501
-        (10, 1, 1, 1, 1, 10, True),
+        # slot_to_epoch(attestation_data.slot + 1, slots_per_epoch) >= current_epoch
+        (23, 2, 3, 1, 2, 8, True),  # attestation_data.justified_epoch == justified_epoch
+        (23, 1, 3, 1, 2, 8, False),  # attestation_data.justified_epoch != justified_epoch
+        # slot_to_epoch(attestation_data.slot + 1, slots_per_epoch) < current_epoch
+        (22, 1, 3, 1, 2, 8, True),  # attestation_data.justified_epoch == previous_justified_epoch
+        (22, 2, 3, 1, 2, 8, False),  # attestation_data.justified_epoch != previous_justified_epoch
     ]
 )
 def test_validate_attestation_justified_epoch(
@@ -114,6 +113,7 @@ def test_validate_attestation_justified_epoch(
     )
 
     if is_valid:
+        # slot_to_epoch(attestation_data.slot + 1, slots_per_epoch) >= current_epoch
         validate_attestation_justified_epoch(
             attestation_data,
             current_epoch,