diff --git a/config/seeds.js b/config/seeds.js
index 47ce148..90badf1 100644
--- a/config/seeds.js
+++ b/config/seeds.js
@@ -1,10 +1,12 @@
 let contractCalls = {
-  Operator: {
+  Contributors: {
     addContributor: [
       // make sure to use an IPFS hash of one of the objects in ipfsContent
       ['0x24dd2aedd8a9fe52ac071b3a23b2fc8f225c185e', '0x272bbfc66166f26cae9c9b96b7f9590e095f02edf342ac2dd71e1667a12116ca', 18, 32, true], // QmQyZJT9uikzDYTZLhhyVZ5ReZVCoMucYzyvDokDJsijhj
       ['0xa502eb4021f3b9ab62f75b57a94e1cfbf81fd827', '0x9569ed44826286597982e40bbdff919c6b7752e29d13250efca452644e6b4b25', 18, 32, true] // QmYPu8zvtfDy18ZqHCviVxnKtxycw5UTJLJyk9oAEjWfnL
-    ],
+    ]
+  },
+  Operator: {
     addProposal: [
       [1, 23, '0x1e1a168d736fc825213144973a8fd5b3cc9f37ad821a8b3d9c3488034bbf69d8', 18, 32], // QmQNA1hhVyL1Vm6HiRxXe9xmc6LUMBDyiNMVgsjThtyevs"
       [2, 42, '0x1e1a168d736fc825213144973a8fd5b3cc9f37ad821a8b3d9c3488034bbf69d8', 18, 32], // QmQNA1hhVyL1Vm6HiRxXe9xmc6LUMBDyiNMVgsjThtyevs"
diff --git a/contracts/Contributors.sol b/contracts/Contributors.sol
index b595c60..eeec329 100644
--- a/contracts/Contributors.sol
+++ b/contracts/Contributors.sol
@@ -23,6 +23,11 @@ contract Contributors is Upgradeable {
   event ContributorAddressUpdated(uint id, address oldAddress, address newAddress);
   event ContributorAdded(uint id, address _address);
 
+  modifier onlyCoreOrOperator() {
+    require(msg.sender == registry.getProxyFor('Operator') || addressIsCore(msg.sender));
+    _;
+  }
+
   function initialize(address sender) public payable {
     require(msg.sender == address(registry));
     uint _id = 1;
@@ -44,14 +49,14 @@ contract Contributors is Upgradeable {
     return count;
   }
 
-  function updateContributorAddress(uint _id, address _oldAddress, address _newAddress) public onlyRegistryContractFor('Operator') {
+  function updateContributorAddress(uint _id, address _oldAddress, address _newAddress) public onlyCoreOrOperator {
     contributorIds[_oldAddress] = 0;
     contributorIds[_newAddress] = _id;
     contributors[_id].account = _newAddress;
     ContributorAddressUpdated(_id, _oldAddress, _newAddress);
   }
 
-  function updateContributorIpfsHash(uint _id, bytes32 _ipfsHash, uint8 _hashFunction, uint8 _hashSize) public onlyRegistryContractFor('Operator') {
+  function updateContributorIpfsHash(uint _id, bytes32 _ipfsHash, uint8 _hashFunction, uint8 _hashSize) public onlyCoreOrOperator {
     Contributor storage c = contributors[_id];
     bytes32 _oldIpfsHash = c.ipfsHash;
     c.ipfsHash = _ipfsHash;
@@ -61,22 +66,21 @@ contract Contributors is Upgradeable {
     ContributorProfileUpdated(_id, _oldIpfsHash, c.ipfsHash);
   }
 
-  function addContributor(address _address, bytes32 _ipfsHash, uint8 _hashFunction, uint8 _hashSize, bool isCore) public onlyRegistryContractFor('Operator') {
+  function addContributor(address _address, bytes32 _ipfsHash, uint8 _hashFunction, uint8 _hashSize, bool _isCore) public onlyCoreOrOperator {
+    require(!addressExists(_address));
     uint _id = contributorsCount + 1;
-    if (contributors[_id].exists != true) {
-      Contributor storage c = contributors[_id];
-      c.exists = true;
-      c.isCore = isCore;
-      c.hashFunction = _hashFunction;
-      c.hashSize = _hashSize;
-      c.ipfsHash = _ipfsHash;
-      c.account = _address;
-      contributorIds[_address] = _id;
+    assert(!contributors[_id].exists); // this can not be acually
+    Contributor storage c = contributors[_id];
+    c.exists = true;
+    c.isCore = _isCore;
+    c.hashFunction = _hashFunction;
+    c.hashSize = _hashSize;
+    c.ipfsHash = _ipfsHash;
+    c.account = _address;
+    contributorIds[_address] = _id;
 
-      contributorsCount += 1;
-
-      ContributorAdded(_id, _address);
-    }
+    contributorsCount += 1;
+    ContributorAdded(_id, _address);
   }
 
   function isCore(uint _id) view public returns (bool) {
diff --git a/scripts/add-contributor.js b/scripts/add-contributor.js
index 1ea00ee..e003bd9 100644
--- a/scripts/add-contributor.js
+++ b/scripts/add-contributor.js
@@ -30,7 +30,7 @@ module.exports = function(callback) {
     let ipfsHash = process.argv[5] || 'QmQyZJT9uikzDYTZLhhyVZ5ReZVCoMucYzyvDokDJsijhj';
     let contributorMultihash = getBytes32FromMultiash(ipfsHash);
     let isCore = true;
-    let contributorResult = await operator.addContributor(contributorToAddAddress, contributorMultihash.digest, contributorMultihash.hashFunction, contributorMultihash.size, isCore);
+    let contributorResult = await contributors.addContributor(contributorToAddAddress, contributorMultihash.digest, contributorMultihash.hashFunction, contributorMultihash.size, isCore);
     console.log('Contributor added, tx: ', contributorResult.tx);
 
     let contributorId = await contributors.getContributorIdByAddress(contributorToAddAddress);
@@ -39,7 +39,7 @@ module.exports = function(callback) {
     console.log('Proposal added, tx: ', proposalResult.tx);
 
     let proposalId = await operator.proposalsCount();
-    let votingResult = operator.vote(proposalId.toNumber()-1);
+    let votingResult = await operator.vote(proposalId.toNumber()-1);
     console.log('Voted for proposal', proposalId.toString(), votingResult.tx);
 
     callback();