diff --git a/specs/core/0_beacon-chain.md b/specs/core/0_beacon-chain.md
index 622eabaf8..b75f14153 100644
--- a/specs/core/0_beacon-chain.md
+++ b/specs/core/0_beacon-chain.md
@@ -647,7 +647,7 @@ def get_previous_epoch(state: BeaconState) -> Epoch:
     Return the current epoch if it's genesis epoch.
     """
     current_epoch = get_current_epoch(state)
-    return (current_epoch - 1) if current_epoch > GENESIS_EPOCH else current_epoch
+    return GENESIS_EPOCH if current_epoch == GENESIS_EPOCH else current_epoch - 1
 ```
 
 ### `get_current_epoch`