diff --git a/configs/mainnet/altair.yaml b/configs/mainnet/altair.yaml
index 6fbd4d4c8..2a2552da4 100644
--- a/configs/mainnet/altair.yaml
+++ b/configs/mainnet/altair.yaml
@@ -40,7 +40,7 @@ DOMAIN_CONTRIBUTION_AND_PROOF: 0x09000000
 # 0x01000000
 ALTAIR_FORK_VERSION: 0x01000000
 # TBD
-ALTAIR_FORK_SLOT: 0
+ALTAIR_FORK_SLOT: 18446744073709551615
 
 
 # Sync protocol
diff --git a/configs/minimal/altair.yaml b/configs/minimal/altair.yaml
index 9aab21a2e..b852e13c0 100644
--- a/configs/minimal/altair.yaml
+++ b/configs/minimal/altair.yaml
@@ -40,7 +40,7 @@ DOMAIN_CONTRIBUTION_AND_PROOF: 0x09000000
 # [customized] Highest byte set to 0x01 to avoid collisions with mainnet versioning
 ALTAIR_FORK_VERSION: 0x01000001
 # [customized]
-ALTAIR_FORK_SLOT: 0
+ALTAIR_FORK_SLOT: 18446744073709551615
 
 
 # Sync protocol
diff --git a/specs/altair/fork.md b/specs/altair/fork.md
index df85f7c3c..b51466c1e 100644
--- a/specs/altair/fork.md
+++ b/specs/altair/fork.md
@@ -26,7 +26,7 @@ Warning: this configuration is not definitive.
 | Name | Value |
 | - | - |
 | `ALTAIR_FORK_VERSION` | `Version('0x01000000')` |
-| `ALTAIR_FORK_SLOT` | `Slot(0)` **TBD** |
+| `ALTAIR_FORK_SLOT` | `Slot(18446744073709551615)` **TBD** |
 
 ## Fork to Altair