diff --git a/specs/core/0_beacon-chain.md b/specs/core/0_beacon-chain.md
index 8991961c7..08f89de2a 100644
--- a/specs/core/0_beacon-chain.md
+++ b/specs/core/0_beacon-chain.md
@@ -138,7 +138,7 @@ An `AttestationRecord` has the following fields:
 
 ```python
 {
-    data: AttestationSignedData
+   data: AttestationSignedData,
     # Attester participation bitfield
     'attester_bitfield': 'bytes',
     # Proof of custody bitfield