diff --git a/specs/core/0_beacon-chain.md b/specs/core/0_beacon-chain.md
index baf5ca198..dca6a0f36 100644
--- a/specs/core/0_beacon-chain.md
+++ b/specs/core/0_beacon-chain.md
@@ -694,9 +694,9 @@ def get_deposit_root() -> bytes32:
 
 @public
 @constant
-def get_merkle_branch(index: uint256) -> bytes32[32]: # size is DEPOSIT_CONTRACT_TREE_DEPTH (symbolic const not supported)
+def get_merkle_branch(deposit_count: uint256) -> bytes32[32]: # size is DEPOSIT_CONTRACT_TREE_DEPTH (symbolic const not supported)
     branch: bytes32[32] # size is DEPOSIT_CONTRACT_TREE_DEPTH
-    index = index + TWO_TO_POWER_OF_TREE_DEPTH
+    index: uint256 = deposit_count + TWO_TO_POWER_OF_TREE_DEPTH
     for i in range(DEPOSIT_CONTRACT_TREE_DEPTH):
         branch[i] = self.deposit_tree[bitwise_xor(index, 1)]
         index /= 2