diff --git a/test_libs/pyspec/eth2spec/test/phase_0/block_processing/test_process_deposit.py b/test_libs/pyspec/eth2spec/test/phase_0/block_processing/test_process_deposit.py
index 63b94c638..a40c120fb 100644
--- a/test_libs/pyspec/eth2spec/test/phase_0/block_processing/test_process_deposit.py
+++ b/test_libs/pyspec/eth2spec/test/phase_0/block_processing/test_process_deposit.py
@@ -183,7 +183,7 @@ def test_bad_merkle_proof(spec, state):
     deposit = prepare_state_and_deposit(spec, state, validator_index, amount)
 
     # mess up merkle branch
-    deposit.proof[-1] = spec.ZERO_HASH
+    deposit.proof[5] = spec.ZERO_HASH
 
     sign_deposit_data(spec, state, deposit.data, privkeys[validator_index])