diff --git a/deposit_contract/contracts/validator_registration.json b/deposit_contract/contracts/validator_registration.json
index 676bf470ab..1779423d2a 100644
--- a/deposit_contract/contracts/validator_registration.json
+++ b/deposit_contract/contracts/validator_registration.json
@@ -1 +1 @@
-{"abi": [{"name": "Deposit", "inputs": [{"type": "bytes", "name": "pubkey", "indexed": false}, {"type": "bytes", "name": "withdrawal_credentials", "indexed": false}, {"type": "bytes", "name": "amount", "indexed": false}, {"type": "bytes", "name": "signature", "indexed": false}], "anonymous": false, "type": "event"}, {"outputs": [], "inputs": [], "constant": false, "payable": false, "type": "constructor"}, {"name": "to_little_endian_64", "outputs": [{"type": "bytes", "name": "out"}], "inputs": [{"type": "uint256", "name": "value"}], "constant": true, "payable": false, "type": "function", "gas": 6973}, {"name": "get_deposit_root", "outputs": [{"type": "bytes32", "name": "out"}], "inputs": [], "constant": true, "payable": false, "type": "function", "gas": 79221}, {"name": "get_deposit_count", "outputs": [{"type": "bytes", "name": "out"}], "inputs": [], "constant": true, "payable": false, "type": "function", "gas": 10922}, {"name": "deposit", "outputs": [], "inputs": [{"type": "bytes", "name": "pubkey"}, {"type": "bytes", "name": "withdrawal_credentials"}, {"type": "bytes", "name": "signature"}], "constant": false, "payable": true, "type": "function", "gas": 1318334}], "bytecode": 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\ No newline at end of file
+{"abi": [{"name": "Deposit", "inputs": [{"type": "bytes", "name": "pubkey", "indexed": false}, {"type": "bytes", "name": "withdrawal_credentials", "indexed": false}, {"type": "bytes", "name": "amount", "indexed": false}, {"type": "bytes", "name": "signature", "indexed": false}, {"type": "bytes", "name": "index", "indexed": false}], "anonymous": false, "type": "event"}, {"outputs": [], "inputs": [], "constant": false, "payable": false, "type": "constructor"}, {"name": "get_deposit_root", "outputs": [{"type": "bytes32", "name": "out"}], "inputs": [], "constant": true, "payable": false, "type": "function", "gas": 79221}, {"name": "get_deposit_count", "outputs": [{"type": "bytes", "name": "out"}], "inputs": [], "constant": true, "payable": false, "type": "function", "gas": 10433}, {"name": "deposit", "outputs": [], "inputs": [{"type": "bytes", "name": "pubkey"}, {"type": "bytes", "name": "withdrawal_credentials"}, {"type": "bytes", "name": "signature"}], "constant": false, "payable": true, "type": "function", "gas": 1334984}], "bytecode": 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\ No newline at end of file
diff --git a/deposit_contract/contracts/validator_registration.v.py b/deposit_contract/contracts/validator_registration.v.py
index 8510380ee2..10daf42b93 100644
--- a/deposit_contract/contracts/validator_registration.v.py
+++ b/deposit_contract/contracts/validator_registration.v.py
@@ -11,6 +11,7 @@
     withdrawal_credentials: bytes[32],
     amount: bytes[8],
     signature: bytes[96],
+    index: bytes[8],
 })
 
 branch: bytes32[DEPOSIT_CONTRACT_TREE_DEPTH]
@@ -24,7 +25,7 @@ def __init__():
         self.zero_hashes[i + 1] = sha256(concat(self.zero_hashes[i], self.zero_hashes[i]))
 
 
-@public
+@private
 @constant
 def to_little_endian_64(value: uint256) -> bytes[8]:
     # Reversing bytes using bitwise uint256 manipulations
@@ -87,6 +88,9 @@ def deposit(pubkey: bytes[PUBKEY_LENGTH],
         sha256(concat(amount, slice(zero_bytes32, start=0, len=32 - AMOUNT_LENGTH), signature_root)),
     ))
 
+    # Emit `Deposit` log
+    log.Deposit(pubkey, withdrawal_credentials, amount, signature, self.to_little_endian_64(self.deposit_count))
+
     # Add `DepositData` root to Merkle tree (update a single `branch` node)
     self.deposit_count += 1
     size: uint256 = self.deposit_count
@@ -97,5 +101,3 @@ def deposit(pubkey: bytes[PUBKEY_LENGTH],
         node = sha256(concat(self.branch[height], node))
         size /= 2
 
-    # Emit `Deposit` log
-    log.Deposit(pubkey, withdrawal_credentials, amount, signature)
diff --git a/deposit_contract/tests/contracts/test_deposit.py b/deposit_contract/tests/contracts/test_deposit.py
index 12f3e7f8bb..783af33567 100644
--- a/deposit_contract/tests/contracts/test_deposit.py
+++ b/deposit_contract/tests/contracts/test_deposit.py
@@ -49,28 +49,6 @@ def deposit_input():
     )
 
 
-@pytest.mark.parametrize(
-    'value,success',
-    [
-        (0, True),
-        (10, True),
-        (55555, True),
-        (2**64 - 1, True),
-        # (2**64, True),  # Note that all calls to `to_little_endian_64` have an input less than 2**64
-    ]
-)
-def test_to_little_endian_64(registration_contract, value, success, assert_tx_failed):
-    call = registration_contract.functions.to_little_endian_64(value)
-
-    if success:
-        little_endian_64 = call.call()
-        assert little_endian_64 == (value).to_bytes(8, 'little')
-    else:
-        assert_tx_failed(
-            lambda: call.call()
-        )
-
-
 @pytest.mark.parametrize(
     'success,deposit_amount',
     [
@@ -151,7 +129,7 @@ def test_deposit_log(registration_contract, a0, w3, deposit_input):
         assert log['withdrawal_credentials'] == deposit_input[1]
         assert log['amount'] == deposit_amount_list[i].to_bytes(8, 'little')
         assert log['signature'] == deposit_input[2]
-
+        assert log['index'] == i.to_bytes(8, 'little')
 
 def test_deposit_tree(registration_contract, w3, assert_tx_failed, deposit_input):
     log_filter = registration_contract.events.Deposit.createFilter(
@@ -171,6 +149,8 @@ def test_deposit_tree(registration_contract, w3, assert_tx_failed, deposit_input
         assert len(logs) == 1
         log = logs[0]['args']
 
+        assert log["index"] == i.to_bytes(8, 'little')
+
         deposit_data = DepositData(
             pubkey=deposit_input[0],
             withdrawal_credentials=deposit_input[1],