diff --git a/specs/core/0_beacon-chain.md b/specs/core/0_beacon-chain.md
index ace489f17..beafa9372 100644
--- a/specs/core/0_beacon-chain.md
+++ b/specs/core/0_beacon-chain.md
@@ -1077,7 +1077,9 @@ def is_double_vote(attestation_data_1: AttestationData,
     Returns True if the provided ``AttestationData`` are slashable
     due to a 'double vote'.
     """
-    return attestation_data_1.slot == attestation_data_2.slot
+    target_epoch_1 = attestation_data_1.slot // EPOCH_LENGTH
+    target_epoch_2 = attestation_data_2.slot // EPOCH_LENGTH
+    return target_epoch_1 == target_epoch_2
 ```
 
 #### `is_surround_vote`
@@ -1092,10 +1094,14 @@ def is_surround_vote(attestation_data_1: AttestationData,
     Note: parameter order matters as this function only checks
     that ``attestation_data_1`` surrounds ``attestation_data_2``.
     """
+    source_epoch_1 = attestation_data_1.justified_slot // EPOCH_LENGTH
+    source_epoch_2 = attestation_data_2.justified_slot // EPOCH_LENGTH
+    target_epoch_1 = attestation_data_1.slot // EPOCH_LENGTH
+    target_epoch_2 = attestation_data_2.slot // EPOCH_LENGTH
     return (
-        (attestation_data_1.justified_slot < attestation_data_2.justified_slot) and
-        (attestation_data_2.justified_slot + 1 == attestation_data_2.slot) and
-        (attestation_data_2.slot < attestation_data_1.slot)
+        (source_epoch_1 < source_epoch_2) and
+        (source_epoch_2 + 1 == target_epoch_2) and
+        (target_epoch_2 < target_epoch_1)
     )
 ```