diff --git a/specs/core/0_beacon-chain.md b/specs/core/0_beacon-chain.md
index bb3d5269ce..9c92356229 100644
--- a/specs/core/0_beacon-chain.md
+++ b/specs/core/0_beacon-chain.md
@@ -1015,7 +1015,7 @@ def get_beacon_proposer_index(state: BeaconState,
     assert previous_epoch <= epoch <= next_epoch
 
     first_committee, _ = get_crosslink_committees_at_slot(state, slot, registry_change)[0]
-    return first_committee[slot % len(first_committee)]
+    return first_committee[epoch % len(first_committee)]
 ```
 
 ### `verify_merkle_branch`