diff --git a/test_libs/pyspec/eth2spec/test/helpers/deposits.py b/test_libs/pyspec/eth2spec/test/helpers/deposits.py
index 7f5975dd4..99c39211e 100644
--- a/test_libs/pyspec/eth2spec/test/helpers/deposits.py
+++ b/test_libs/pyspec/eth2spec/test/helpers/deposits.py
@@ -43,14 +43,14 @@ def build_deposit(spec,
                   withdrawal_credentials,
                   signed):
     deposit_data = build_deposit_data(spec, pubkey, privkey, amount, withdrawal_credentials, state=state, signed=signed)
-    deposit_data_list.append(deposit_data)
     index = len(deposit_data_list)
+    deposit_data_list.append(deposit_data)
     root = hash_tree_root(List[spec.DepositData, 2**spec.DEPOSIT_CONTRACT_TREE_DEPTH](*deposit_data_list))
     tree = calc_merkle_tree_from_leaves(tuple([d.hash_tree_root() for d in deposit_data_list]))
-    proof = list(get_merkle_proof(tree, item_index=index)) + [index.to_bytes(32, 'little')]
+    proof = list(get_merkle_proof(tree, item_index=index)) + [(index + 1).to_bytes(32, 'little')]
     leaf = deposit_data.hash_tree_root()
     assert spec.verify_merkle_branch(leaf, proof, spec.DEPOSIT_CONTRACT_TREE_DEPTH + 1, index, root)
-    deposit = spec.Deposit(proof, index, deposit_data)
+    deposit = spec.Deposit(proof=proof, data=deposit_data)
 
     return deposit, root, deposit_data_list