diff --git a/specs/core/0_beacon-chain.md b/specs/core/0_beacon-chain.md
index 023d64339..801be22f0 100644
--- a/specs/core/0_beacon-chain.md
+++ b/specs/core/0_beacon-chain.md
@@ -1789,7 +1789,7 @@ def get_current_total_balance(state: BeaconState) -> Gwei:
 
 ```python
 def get_previous_total_balance(state: BeaconState) -> Gwei:
-    return get_total_balance(state, get_active_validator_indices(state.validator_registry, previous_epoch))
+    return get_total_balance(state, get_active_validator_indices(state.validator_registry, get_previous_epoch(state)))
 ```
 
 ```python