diff --git a/specs/core/0_beacon-chain.md b/specs/core/0_beacon-chain.md
index 1f2f5c9c5..ef1b27235 100644
--- a/specs/core/0_beacon-chain.md
+++ b/specs/core/0_beacon-chain.md
@@ -699,7 +699,7 @@ def min_empty_validator(validators: List[ValidatorRecord], current_slot: int):
 ```
 
 ```python
-def get_fork_version(state: State, slot: uint64):
+def get_fork_version(state: State, slot: int) -> int:
     return state.pre_fork_version if slot < state.fork_slot_number else state.post_fork_version
 ```