diff --git a/configs/mainnet/altair.yaml b/configs/mainnet/altair.yaml
index 46b74b3aa..03b59335b 100644
--- a/configs/mainnet/altair.yaml
+++ b/configs/mainnet/altair.yaml
@@ -12,16 +12,16 @@ PROPORTIONAL_SLASHING_MULTIPLIER_ALTAIR: 2
 
 # Misc
 # ---------------------------------------------------------------
-# 2**10 (= 1,024)
-SYNC_COMMITTEE_SIZE: 1024
+# 2**9 (= 512)
+SYNC_COMMITTEE_SIZE: 512
 # 2**2 (= 4)
 INACTIVITY_SCORE_BIAS: 4
 
 
 # Time parameters
 # ---------------------------------------------------------------
-# 2**8 (= 256)
-EPOCHS_PER_SYNC_COMMITTEE_PERIOD: 256
+# 2**9 (= 512)
+EPOCHS_PER_SYNC_COMMITTEE_PERIOD: 512
 
 
 # Signature domains
diff --git a/specs/altair/beacon-chain.md b/specs/altair/beacon-chain.md
index 7ff6cd339..b2ee93557 100644
--- a/specs/altair/beacon-chain.md
+++ b/specs/altair/beacon-chain.md
@@ -118,14 +118,14 @@ This patch updates a few configuration values to move penalty parameters closer
 
 | Name | Value |
 | - | - |
-| `SYNC_COMMITTEE_SIZE` | `uint64(2**10)` (= 1,024) |
+| `SYNC_COMMITTEE_SIZE` | `uint64(2**9)` (= 512) |
 | `INACTIVITY_SCORE_BIAS` | `uint64(4)` |
 
 ### Time parameters
 
 | Name | Value | Unit | Duration |
 | - | - | :-: | :-: |
-| `EPOCHS_PER_SYNC_COMMITTEE_PERIOD` | `Epoch(2**8)` (= 256) | epochs | ~27 hours |
+| `EPOCHS_PER_SYNC_COMMITTEE_PERIOD` | `uint64(2**9)` (= 512) | epochs | ~54 hours |
 
 ### Domain types