diff --git a/contracts/access/roles/WhitelistAdminRole.sol b/contracts/access/roles/WhitelistAdminRole.sol
index 8af7412ba..e8bc0ab48 100644
--- a/contracts/access/roles/WhitelistAdminRole.sol
+++ b/contracts/access/roles/WhitelistAdminRole.sol
@@ -1,12 +1,14 @@
 pragma solidity ^0.5.0;
 
+import "zos-lib/contracts/Initializable.sol";
+
 import "../Roles.sol";
 
 /**
  * @title WhitelistAdminRole
  * @dev WhitelistAdmins are responsible for assigning and removing Whitelisted accounts.
  */
-contract WhitelistAdminRole {
+contract WhitelistAdminRole is Initializable {
     using Roles for Roles.Role;
 
     event WhitelistAdminAdded(address indexed account);
@@ -14,8 +16,10 @@ contract WhitelistAdminRole {
 
     Roles.Role private _whitelistAdmins;
 
-    constructor () internal {
-        _addWhitelistAdmin(msg.sender);
+    function _initialize(address sender) internal initializer {
+        if (!isWhitelistAdmin(sender)) {
+            _addWhitelistAdmin(sender);
+        }
     }
 
     modifier onlyWhitelistAdmin() {
diff --git a/contracts/access/roles/WhitelistedRole.sol b/contracts/access/roles/WhitelistedRole.sol
index 3ba5ae0cf..87b146b95 100644
--- a/contracts/access/roles/WhitelistedRole.sol
+++ b/contracts/access/roles/WhitelistedRole.sol
@@ -1,5 +1,7 @@
 pragma solidity ^0.5.0;
 
+import "zos-lib/contracts/Initializable.sol";
+
 import "../Roles.sol";
 import "./WhitelistAdminRole.sol";
 
@@ -9,7 +11,7 @@ import "./WhitelistAdminRole.sol";
  * crowdsale). This role is special in that the only accounts that can add it are WhitelistAdmins (who can also remove
  * it), and not Whitelisteds themselves.
  */
-contract WhitelistedRole is WhitelistAdminRole {
+contract WhitelistedRole is Initializable, WhitelistAdminRole {
     using Roles for Roles.Role;
 
     event WhitelistedAdded(address indexed account);
@@ -22,6 +24,10 @@ contract WhitelistedRole is WhitelistAdminRole {
         _;
     }
 
+    function _initialize(address sender) internal initializer {
+        WhitelistAdminRole._initialize(sender);
+    }
+
     function isWhitelisted(address account) public view returns (bool) {
         return _whitelisteds.has(account);
     }
diff --git a/contracts/crowdsale/Crowdsale.sol b/contracts/crowdsale/Crowdsale.sol
index 2ab365033..87a1d91d9 100644
--- a/contracts/crowdsale/Crowdsale.sol
+++ b/contracts/crowdsale/Crowdsale.sol
@@ -54,7 +54,7 @@ contract Crowdsale is Initializable, ReentrancyGuard {
      * @param wallet Address where collected funds will be forwarded to
      * @param token Address of the token being sold
      */
-    function initialize(uint256 rate, address wallet, IERC20 token) public initializer {
+    function initialize(uint256 rate, address payable wallet, IERC20 token) public initializer {
         require(rate > 0);
         require(wallet != address(0));
         require(address(token) != address(0));
@@ -128,7 +128,7 @@ contract Crowdsale is Initializable, ReentrancyGuard {
     }
 
     function _hasBeenInitialized() internal view returns (bool) {
-        return ((_rate > 0) && (_wallet != address(0)) && (_token != address(0)));
+        return ((_rate > 0) && (_wallet != address(0)) && (address(_token) != address(0)));
     }
 
     /**
diff --git a/contracts/crowdsale/validation/WhitelistCrowdsale.sol b/contracts/crowdsale/validation/WhitelistCrowdsale.sol
index 16e28786e..29e13b617 100644
--- a/contracts/crowdsale/validation/WhitelistCrowdsale.sol
+++ b/contracts/crowdsale/validation/WhitelistCrowdsale.sol
@@ -7,7 +7,11 @@ import "../../access/roles/WhitelistedRole.sol";
  * @title WhitelistCrowdsale
  * @dev Crowdsale in which only whitelisted users can contribute.
  */
-contract WhitelistCrowdsale is WhitelistedRole, Crowdsale {
+contract WhitelistCrowdsale is Initializable, WhitelistedRole, Crowdsale {
+    function initialize(address sender) public initializer {
+        WhitelistedRole._initialize(sender);
+    }
+
     /**
     * @dev Extend parent behavior requiring beneficiary to be whitelisted. Note that no
     * restriction is imposed on the account sending the transaction.
diff --git a/contracts/drafts/TokenVesting.sol b/contracts/drafts/TokenVesting.sol
index d4839f7ae..623c37a4a 100644
--- a/contracts/drafts/TokenVesting.sol
+++ b/contracts/drafts/TokenVesting.sol
@@ -47,7 +47,7 @@ contract TokenVesting is Initializable, Ownable {
      * @param duration duration in seconds of the period in which the tokens will vest
      * @param revocable whether the vesting is revocable or not
      */
-    constructor (address beneficiary, uint256 start, uint256 cliffDuration, uint256 duration, bool revocable, address sender) public initializer {
+    function initialize(address beneficiary, uint256 start, uint256 cliffDuration, uint256 duration, bool revocable, address sender) public initializer {
         Ownable.initialize(sender);
 
         require(beneficiary != address(0));
diff --git a/contracts/examples/StandardToken.sol b/contracts/examples/StandardToken.sol
index e004a2562..b024ea49c 100644
--- a/contracts/examples/StandardToken.sol
+++ b/contracts/examples/StandardToken.sol
@@ -1,4 +1,4 @@
-pragma solidity ^0.4.24;
+pragma solidity ^0.5.0;
 
 import "zos-lib/contracts/Initializable.sol";
 import "../token/ERC20/ERC20Detailed.sol";
@@ -12,8 +12,8 @@ import "../token/ERC20/ERC20Pausable.sol";
  */
 contract StandardToken is Initializable, ERC20Detailed, ERC20Mintable, ERC20Pausable {
     function initialize(
-        string name, string symbol, uint8 decimals, uint256 initialSupply, address initialHolder, 
-        address[] minters, address[] pausers
+        string memory name, string memory symbol, uint8 decimals, uint256 initialSupply, address initialHolder, 
+        address[] memory minters, address[] memory pausers
     ) public initializer {
         ERC20Detailed.initialize(name, symbol, decimals);
 
@@ -35,7 +35,7 @@ contract StandardToken is Initializable, ERC20Detailed, ERC20Mintable, ERC20Paus
             _addMinter(minters[i]);
         }
 
-        for (i = 0; i < pausers.length; ++i) {
+        for (uint256 i = 0; i < pausers.length; ++i) {
             _addPauser(pausers[i]);
         }
     }
diff --git a/contracts/introspection/ERC165.sol b/contracts/introspection/ERC165.sol
index 8666fa2b5..1181d91b7 100644
--- a/contracts/introspection/ERC165.sol
+++ b/contracts/introspection/ERC165.sol
@@ -25,13 +25,13 @@ contract ERC165 is Initializable, IERC165 {
      * implement ERC165 itself
      */
     function initialize() public initializer {
-        _registerInterface(_InterfaceId_ERC165);
+        _registerInterface(_INTERFACE_ID_ERC165);
     }
 
     /**
      * @dev implement supportsInterface(bytes4) using a lookup table
      */
-    function supportsInterface(bytes4 interfaceId) external view returns (bool) {
+    function supportsInterface(bytes4 interfaceId) public view returns (bool) {
         return _supportedInterfaces[interfaceId];
     }
 
diff --git a/contracts/mocks/ERC20CappedMock.sol b/contracts/mocks/ERC20CappedMock.sol
index ee0b75425..6be7f8834 100644
--- a/contracts/mocks/ERC20CappedMock.sol
+++ b/contracts/mocks/ERC20CappedMock.sol
@@ -1,4 +1,4 @@
-pragma solidity ^0.4.24;
+pragma solidity ^0.5.0;
 
 import "../token/ERC20/ERC20Capped.sol";
 import "./MinterRoleMock.sol";
diff --git a/contracts/mocks/ERC20MigratorMock.sol b/contracts/mocks/ERC20MigratorMock.sol
index ec7fd691a..24b28b226 100644
--- a/contracts/mocks/ERC20MigratorMock.sol
+++ b/contracts/mocks/ERC20MigratorMock.sol
@@ -1,4 +1,4 @@
-pragma solidity ^0.4.24;
+pragma solidity ^0.5.0;
 
 import "../drafts/ERC20Migrator.sol";
 
diff --git a/contracts/mocks/ERC721PausableMock.sol b/contracts/mocks/ERC721PausableMock.sol
index 26c1cb4b2..5e64396ca 100644
--- a/contracts/mocks/ERC721PausableMock.sol
+++ b/contracts/mocks/ERC721PausableMock.sol
@@ -8,7 +8,7 @@ import "./PauserRoleMock.sol";
  * This mock just provides a public mint, burn and exists functions for testing purposes
  */
 contract ERC721PausableMock is ERC721Pausable, PauserRoleMock {
-    constructor() {
+    constructor() public {
         ERC721.initialize();
         ERC721Pausable.initialize(msg.sender);
     }
diff --git a/contracts/mocks/EscrowMock.sol b/contracts/mocks/EscrowMock.sol
index f156307fc..20f33f985 100644
--- a/contracts/mocks/EscrowMock.sol
+++ b/contracts/mocks/EscrowMock.sol
@@ -1,6 +1,6 @@
-pragma solidity ^0.4.24;
+pragma solidity ^0.5.0;
 
-import "../payment/Escrow.sol";
+import "../payment/escrow/Escrow.sol";
 
 contract EscrowMock is Escrow {
     constructor() public {
diff --git a/contracts/mocks/ForceEther.sol b/contracts/mocks/ForceEther.sol
index dd4e7bf7c..9ac81d0e4 100644
--- a/contracts/mocks/ForceEther.sol
+++ b/contracts/mocks/ForceEther.sol
@@ -1,4 +1,4 @@
-pragma solidity ^0.4.24;
+pragma solidity ^0.5.0;
 
 
 // @title Force Ether into a contract.
@@ -10,7 +10,7 @@ contract ForceEther {
 
     constructor() public payable { }
 
-    function destroyAndSend(address recipient) public {
+    function destroyAndSend(address payable recipient) public {
         selfdestruct(recipient);
     }
 }
diff --git a/contracts/mocks/MessageHelper.sol b/contracts/mocks/MessageHelper.sol
index a73ce3bec..2afd680bb 100644
--- a/contracts/mocks/MessageHelper.sol
+++ b/contracts/mocks/MessageHelper.sol
@@ -1,4 +1,4 @@
-pragma solidity ^0.4.24;
+pragma solidity ^0.5.0;
 
 
 contract MessageHelper {
@@ -9,7 +9,7 @@ contract MessageHelper {
     function showMessage(
         bytes32 _message,
         uint256 _number,
-        string _text
+        string memory _text
     )
         public
         returns (bool)
@@ -21,7 +21,7 @@ contract MessageHelper {
     function buyMessage(
         bytes32 _message,
         uint256 _number,
-        string _text
+        string memory _text
     )
         public
         payable
@@ -39,9 +39,10 @@ contract MessageHelper {
         require(false);
     }
 
-    function call(address _to, bytes _data) public returns (bool) {
+    function call(address _to, bytes memory _data) public returns (bool) {
         // solium-disable-next-line security/no-low-level-calls
-        if (_to.call(_data))
+        (bool success,) = _to.call(_data);
+        if (success)
             return true;
         else
             return false;
diff --git a/contracts/mocks/OwnableMock.sol b/contracts/mocks/OwnableMock.sol
index 54d62f6dd..49726ab72 100644
--- a/contracts/mocks/OwnableMock.sol
+++ b/contracts/mocks/OwnableMock.sol
@@ -3,7 +3,7 @@ pragma solidity ^0.5.0;
 import "../ownership/Ownable.sol";
 
 contract OwnableMock is Ownable {
-    constructor() {
+    constructor() public {
         Ownable.initialize(msg.sender);
     }
 }
diff --git a/contracts/mocks/PausableCrowdsaleImpl.sol b/contracts/mocks/PausableCrowdsaleImpl.sol
index 11f44c7b8..9ae9399de 100644
--- a/contracts/mocks/PausableCrowdsaleImpl.sol
+++ b/contracts/mocks/PausableCrowdsaleImpl.sol
@@ -4,7 +4,7 @@ import "../token/ERC20/ERC20.sol";
 import "../crowdsale/validation/PausableCrowdsale.sol";
 
 contract PausableCrowdsaleImpl is PausableCrowdsale {
-    constructor (uint256 _rate, address payable _wallet, ERC20 _token) public Crowdsale(_rate, _wallet, _token) {
-        // solhint-disable-previous-line no-empty-blocks
+    constructor (uint256 _rate, address payable _wallet, ERC20 _token) public {
+      Crowdsale.initialize(_rate, _wallet, _token);
     }
 }
diff --git a/contracts/mocks/PaymentSplitterMock.sol b/contracts/mocks/PaymentSplitterMock.sol
index 5a0882ab0..393e3018a 100644
--- a/contracts/mocks/PaymentSplitterMock.sol
+++ b/contracts/mocks/PaymentSplitterMock.sol
@@ -1,9 +1,9 @@
-pragma solidity ^0.4.24;
+pragma solidity ^0.5.0;
 
 import "../payment/PaymentSplitter.sol";
 
 contract PaymentSplitterMock is PaymentSplitter {
-    constructor(address[] payees, uint256[] shares) public {
+    constructor(address[] memory payees, uint256[] memory shares) public {
         PaymentSplitter.initialize(payees, shares);
     }
 }
diff --git a/contracts/mocks/PostDeliveryCrowdsaleImpl.sol b/contracts/mocks/PostDeliveryCrowdsaleImpl.sol
index c9c38fc86..ec4a6da08 100644
--- a/contracts/mocks/PostDeliveryCrowdsaleImpl.sol
+++ b/contracts/mocks/PostDeliveryCrowdsaleImpl.sol
@@ -6,8 +6,6 @@ import "../crowdsale/distribution/PostDeliveryCrowdsale.sol";
 contract PostDeliveryCrowdsaleImpl is PostDeliveryCrowdsale {
     constructor (uint256 openingTime, uint256 closingTime, uint256 rate, address payable wallet, IERC20 token)
         public
-        TimedCrowdsale(openingTime, closingTime)
-        Crowdsale(rate, wallet, token)
     {
         Crowdsale.initialize(rate, wallet, token);
         TimedCrowdsale.initialize(openingTime, closingTime);
diff --git a/contracts/mocks/PullPaymentMock.sol b/contracts/mocks/PullPaymentMock.sol
index 01c883d00..38f093e02 100644
--- a/contracts/mocks/PullPaymentMock.sol
+++ b/contracts/mocks/PullPaymentMock.sol
@@ -5,7 +5,7 @@ import "../payment/PullPayment.sol";
 // mock class using PullPayment
 contract PullPaymentMock is PullPayment {
     constructor () public payable {
-        PullPayment.initialize();
+        PullPayment._initialize();
     }
 
     // test helper function to call asyncTransfer
diff --git a/contracts/mocks/RefundEscrowMock.sol b/contracts/mocks/RefundEscrowMock.sol
index 35e56f809..213c18af2 100644
--- a/contracts/mocks/RefundEscrowMock.sol
+++ b/contracts/mocks/RefundEscrowMock.sol
@@ -1,9 +1,9 @@
-pragma solidity ^0.4.24;
+pragma solidity ^0.5.0;
 
-import "../payment/RefundEscrow.sol";
+import "../payment/escrow/RefundEscrow.sol";
 
 contract RefundEscrowMock is RefundEscrow {
-    constructor(address beneficiary) public {
+    constructor(address payable beneficiary) public {
         RefundEscrow.initialize(beneficiary, msg.sender);
     }
 }
diff --git a/contracts/mocks/RefundablePostDeliveryCrowdsaleImpl.sol b/contracts/mocks/RefundablePostDeliveryCrowdsaleImpl.sol
index b81f0757c..830ffc247 100644
--- a/contracts/mocks/RefundablePostDeliveryCrowdsaleImpl.sol
+++ b/contracts/mocks/RefundablePostDeliveryCrowdsaleImpl.sol
@@ -13,10 +13,9 @@ contract RefundablePostDeliveryCrowdsaleImpl is RefundablePostDeliveryCrowdsale
         uint256 goal
     )
         public
-        Crowdsale(rate, wallet, token)
-        TimedCrowdsale(openingTime, closingTime)
-        RefundableCrowdsale(goal)
     {
-        // solhint-disable-previous-line no-empty-blocks
+        Crowdsale.initialize(rate, wallet, token);
+        TimedCrowdsale.initialize(openingTime, closingTime);
+        RefundableCrowdsale.initialize(goal);
     }
 }
diff --git a/contracts/mocks/SampleCrowdsaleMock.sol b/contracts/mocks/SampleCrowdsaleMock.sol
index 70a4da8e1..7f5143785 100644
--- a/contracts/mocks/SampleCrowdsaleMock.sol
+++ b/contracts/mocks/SampleCrowdsaleMock.sol
@@ -1,4 +1,4 @@
-pragma solidity ^0.4.24;
+pragma solidity ^0.5.0;
 
 import "../examples/SampleCrowdsale.sol";
 
@@ -14,7 +14,7 @@ contract SampleCrowdsaleMock is SampleCrowdsale {
         uint256 openingTime,
         uint256 closingTime,
         uint256 rate,
-        address wallet,
+        address payable wallet,
         uint256 cap,
         ERC20Mintable token,
         uint256 goal
diff --git a/contracts/mocks/SignatureBouncerMock.sol b/contracts/mocks/SignatureBouncerMock.sol
index c764a0a4e..b846d4dde 100644
--- a/contracts/mocks/SignatureBouncerMock.sol
+++ b/contracts/mocks/SignatureBouncerMock.sol
@@ -5,7 +5,7 @@ import "./SignerRoleMock.sol";
 
 contract SignatureBouncerMock is SignatureBouncer, SignerRoleMock {
     constructor() public {
-        SignatureBouncer.initialize(msg.sender);
+        SignatureBouncer._initialize(msg.sender);
     }
 
     function checkValidSignature(address account, bytes memory signature)
diff --git a/contracts/mocks/SimpleTokenMock.sol b/contracts/mocks/SimpleTokenMock.sol
index df8f8b581..11add07cd 100644
--- a/contracts/mocks/SimpleTokenMock.sol
+++ b/contracts/mocks/SimpleTokenMock.sol
@@ -1,4 +1,4 @@
-pragma solidity ^0.4.24;
+pragma solidity ^0.5.0;
 
 import "../examples/SimpleToken.sol";
 
diff --git a/contracts/mocks/TokenTimelockMock.sol b/contracts/mocks/TokenTimelockMock.sol
index c50892d40..7d8fdf566 100644
--- a/contracts/mocks/TokenTimelockMock.sol
+++ b/contracts/mocks/TokenTimelockMock.sol
@@ -1,4 +1,4 @@
-pragma solidity ^0.4.24;
+pragma solidity ^0.5.0;
 
 import "../token/ERC20/TokenTimelock.sol";
 
diff --git a/contracts/mocks/TokenVestingMock.sol b/contracts/mocks/TokenVestingMock.sol
index 44bcb6ed4..cab7fbed8 100644
--- a/contracts/mocks/TokenVestingMock.sol
+++ b/contracts/mocks/TokenVestingMock.sol
@@ -1,4 +1,4 @@
-pragma solidity ^0.4.24;
+pragma solidity ^0.5.0;
 
 import "../drafts/TokenVesting.sol";
 
diff --git a/contracts/mocks/WhitelistAdminRoleMock.sol b/contracts/mocks/WhitelistAdminRoleMock.sol
index 7a267ca21..5c8ffca35 100644
--- a/contracts/mocks/WhitelistAdminRoleMock.sol
+++ b/contracts/mocks/WhitelistAdminRoleMock.sol
@@ -3,6 +3,10 @@ pragma solidity ^0.5.0;
 import "../access/roles/WhitelistAdminRole.sol";
 
 contract WhitelistAdminRoleMock is WhitelistAdminRole {
+    constructor () public {
+        WhitelistAdminRole._initialize(msg.sender);
+    }
+
     function removeWhitelistAdmin(address account) public {
         _removeWhitelistAdmin(account);
     }
diff --git a/contracts/mocks/WhitelistCrowdsaleImpl.sol b/contracts/mocks/WhitelistCrowdsaleImpl.sol
index 0200f7f7f..e17cfdd97 100644
--- a/contracts/mocks/WhitelistCrowdsaleImpl.sol
+++ b/contracts/mocks/WhitelistCrowdsaleImpl.sol
@@ -6,7 +6,8 @@ import "../crowdsale/Crowdsale.sol";
 
 
 contract WhitelistCrowdsaleImpl is Crowdsale, WhitelistCrowdsale {
-    constructor (uint256 _rate, address payable _wallet, IERC20 _token) public Crowdsale(_rate, _wallet, _token) {
-        // solhint-disable-previous-line no-empty-blocks
+    constructor (uint256 _rate, address payable _wallet, IERC20 _token) public {
+        Crowdsale.initialize(_rate, _wallet, _token);
+        WhitelistCrowdsale.initialize(msg.sender);
     }
 }
diff --git a/contracts/payment/PaymentSplitter.sol b/contracts/payment/PaymentSplitter.sol
index 280e4b9ac..82b768ec1 100644
--- a/contracts/payment/PaymentSplitter.sol
+++ b/contracts/payment/PaymentSplitter.sol
@@ -1,5 +1,7 @@
 pragma solidity ^0.5.0;
 
+import "zos-lib/contracts/Initializable.sol";
+
 import "../math/SafeMath.sol";
 
 /**
@@ -7,7 +9,7 @@ import "../math/SafeMath.sol";
  * @dev This contract can be used when payments need to be received by a group
  * of people and split proportionately to some number of shares they own.
  */
-contract PaymentSplitter {
+contract PaymentSplitter is Initializable {
     using SafeMath for uint256;
 
     event PayeeAdded(address account, uint256 shares);
@@ -24,7 +26,7 @@ contract PaymentSplitter {
     /**
      * @dev Constructor
      */
-    constructor (address[] memory payees, uint256[] memory shares) public payable {
+    function initialize(address[] memory payees, uint256[] memory shares) public payable initializer {
         require(payees.length == shares.length);
         require(payees.length > 0);
 
diff --git a/contracts/payment/escrow/ConditionalEscrow.sol b/contracts/payment/escrow/ConditionalEscrow.sol
index 268d731fa..283d59d60 100644
--- a/contracts/payment/escrow/ConditionalEscrow.sol
+++ b/contracts/payment/escrow/ConditionalEscrow.sol
@@ -7,7 +7,11 @@ import "./Escrow.sol";
  * @dev Base abstract escrow to only allow withdrawal if a condition is met.
  * @dev Intended usage: See Escrow.sol. Same usage guidelines apply here.
  */
-contract ConditionalEscrow is Escrow {
+contract ConditionalEscrow is Initializable, Escrow {
+    function initialize(address sender) public initializer {
+        Escrow.initialize(sender);
+    }
+
     /**
     * @dev Returns whether an address is allowed to withdraw their funds. To be
     * implemented by derived contracts.
diff --git a/contracts/payment/escrow/Escrow.sol b/contracts/payment/escrow/Escrow.sol
index c010add45..5ff736cec 100644
--- a/contracts/payment/escrow/Escrow.sol
+++ b/contracts/payment/escrow/Escrow.sol
@@ -15,7 +15,7 @@ import "../../ownership/Secondary.sol";
  * payment method should be its primary, and provide public methods redirecting
  * to the escrow's deposit and withdraw.
  */
-contract Escrow is Secondary {
+contract Escrow is Initializable, Secondary {
     using SafeMath for uint256;
 
     event Deposited(address indexed payee, uint256 weiAmount);
@@ -23,6 +23,10 @@ contract Escrow is Secondary {
 
     mapping(address => uint256) private _deposits;
 
+    function initialize(address sender) public initializer {
+        Secondary.initialize(sender);
+    }
+
     function depositsOf(address payee) public view returns (uint256) {
         return _deposits[payee];
     }
diff --git a/contracts/payment/escrow/RefundEscrow.sol b/contracts/payment/escrow/RefundEscrow.sol
index 0c9cd99a6..ac67f8cc3 100644
--- a/contracts/payment/escrow/RefundEscrow.sol
+++ b/contracts/payment/escrow/RefundEscrow.sol
@@ -1,5 +1,7 @@
 pragma solidity ^0.5.0;
 
+import 'zos-lib/contracts/Initializable.sol';
+
 import "./ConditionalEscrow.sol";
 
 /**
@@ -13,7 +15,7 @@ import "./ConditionalEscrow.sol";
  * with RefundEscrow will be made through the primary contract. See the
  * RefundableCrowdsale contract for an example of RefundEscrow’s use.
  */
-contract RefundEscrow is ConditionalEscrow {
+contract RefundEscrow is Initializable, ConditionalEscrow {
     enum State { Active, Refunding, Closed }
 
     event RefundsClosed();
@@ -26,7 +28,9 @@ contract RefundEscrow is ConditionalEscrow {
      * @dev Constructor.
      * @param beneficiary The beneficiary of the deposits.
      */
-    constructor (address payable beneficiary) public {
+    function initialize(address payable beneficiary, address sender) public initializer {
+        ConditionalEscrow.initialize(sender);
+
         require(beneficiary != address(0));
         _beneficiary = beneficiary;
         _state = State.Active;
diff --git a/contracts/token/ERC20/StandaloneERC20.sol b/contracts/token/ERC20/StandaloneERC20.sol
index 49e831c1d..3aaf81e34 100644
--- a/contracts/token/ERC20/StandaloneERC20.sol
+++ b/contracts/token/ERC20/StandaloneERC20.sol
@@ -1,4 +1,4 @@
-pragma solidity ^0.4.24;
+pragma solidity ^0.5.0;
 
 import "zos-lib/contracts/Initializable.sol";
 import "./ERC20Detailed.sol";
@@ -12,11 +12,9 @@ import "./ERC20Pausable.sol";
  */
 contract StandaloneERC20 is Initializable, ERC20Detailed, ERC20Mintable, ERC20Pausable {
     function initialize(
-        string name, string symbol, uint8 decimals, uint256 initialSupply, address initialHolder,
-        address[] minters, address[] pausers
+        string memory name, string memory symbol, uint8 decimals, uint256 initialSupply, address initialHolder,
+        address[] memory minters, address[] memory pausers
     ) public initializer {
-        require(initialSupply > 0);
-
         ERC20Detailed.initialize(name, symbol, decimals);
 
         // Mint the initial supply
@@ -35,13 +33,13 @@ contract StandaloneERC20 is Initializable, ERC20Detailed, ERC20Mintable, ERC20Pa
             _addMinter(minters[i]);
         }
 
-        for (i = 0; i < pausers.length; ++i) {
+        for (uint256 i = 0; i < pausers.length; ++i) {
             _addPauser(pausers[i]);
         }
     }
 
     function initialize(
-        string name, string symbol, uint8 decimals, address[] minters, address[] pausers
+        string memory name, string memory symbol, uint8 decimals, address[] memory minters, address[] memory pausers
     ) public initializer {
         ERC20Detailed.initialize(name, symbol, decimals);
 
@@ -58,7 +56,7 @@ contract StandaloneERC20 is Initializable, ERC20Detailed, ERC20Mintable, ERC20Pa
             _addMinter(minters[i]);
         }
 
-        for (i = 0; i < pausers.length; ++i) {
+        for (uint256 i = 0; i < pausers.length; ++i) {
             _addPauser(pausers[i]);
         }
     }
diff --git a/contracts/token/ERC721/ERC721Enumerable.sol b/contracts/token/ERC721/ERC721Enumerable.sol
index 5c61280ed..3b9dcc54c 100644
--- a/contracts/token/ERC721/ERC721Enumerable.sol
+++ b/contracts/token/ERC721/ERC721Enumerable.sol
@@ -37,11 +37,11 @@ contract ERC721Enumerable is Initializable, ERC165, ERC721, IERC721Enumerable {
         require(ERC721._hasBeenInitialized());
 
         // register the supported interface to conform to ERC721 via ERC165
-        _registerInterface(_InterfaceId_ERC721Enumerable);
+        _registerInterface(_INTERFACE_ID_ERC721_ENUMERABLE);
     }
 
     function _hasBeenInitialized() internal view returns (bool) {
-        return supportsInterface(_InterfaceId_ERC721Enumerable);
+        return supportsInterface(_INTERFACE_ID_ERC721_ENUMERABLE);
     }
 
     /**
diff --git a/contracts/token/ERC721/ERC721Metadata.sol b/contracts/token/ERC721/ERC721Metadata.sol
index 8ca6d0e2e..0fbb1e6ae 100644
--- a/contracts/token/ERC721/ERC721Metadata.sol
+++ b/contracts/token/ERC721/ERC721Metadata.sol
@@ -36,6 +36,9 @@ contract ERC721Metadata is Initializable, ERC165, ERC721, IERC721Metadata {
         _registerInterface(_INTERFACE_ID_ERC721_METADATA);
     }
 
+  function _hasBeenInitialized() internal view returns (bool) {
+    return supportsInterface(_INTERFACE_ID_ERC721_METADATA);
+}
     /**
      * @dev Gets the token name
      * @return string representing the token name
diff --git a/contracts/token/ERC721/StandaloneERC721.sol b/contracts/token/ERC721/StandaloneERC721.sol
index 49059d8ff..14ec4a9d5 100644
--- a/contracts/token/ERC721/StandaloneERC721.sol
+++ b/contracts/token/ERC721/StandaloneERC721.sol
@@ -1,4 +1,4 @@
-pragma solidity ^0.4.24;
+pragma solidity ^0.5.0;
 
 import "zos-lib/contracts/Initializable.sol";
 import "./ERC721.sol";
@@ -15,7 +15,7 @@ import "./ERC721Pausable.sol";
 contract StandaloneERC721
     is Initializable, ERC721, ERC721Enumerable, ERC721Metadata, ERC721MetadataMintable, ERC721Pausable
 {
-    function initialize(string name, string symbol, address[] minters, address[] pausers) public initializer {
+    function initialize(string memory name, string memory symbol, address[] memory minters, address[] memory pausers) public initializer {
         ERC721.initialize();
         ERC721Enumerable.initialize();
         ERC721Metadata.initialize(name, symbol);
@@ -33,7 +33,7 @@ contract StandaloneERC721
             _addMinter(minters[i]);
         }
 
-        for (i = 0; i < pausers.length; ++i) {
+        for (uint256 i = 0; i < pausers.length; ++i) {
             _addPauser(pausers[i]);
         }
     }
diff --git a/package-lock.json b/package-lock.json
index bd6ba497a..7f1929853 100644
--- a/package-lock.json
+++ b/package-lock.json
@@ -4900,10 +4900,18 @@
               "integrity": "sha512-VU6/DSUX93d1fCzBz7WP/SGCQizO1rKZi4Px9j/3yRyfssHyFcZamMw2/sj4E8TlfMXONvZLoforR8B4bRoyTQ==",
               "dev": true,
               "requires": {
+                "bignumber.js": "git+https://github.com/frozeman/bignumber.js-nolookahead.git#57692b3ecfc98bbdd6b3a516cb2353652ea49934",
                 "crypto-js": "^3.1.4",
                 "utf8": "^2.1.1",
                 "xhr2-cookies": "^1.1.0",
                 "xmlhttprequest": "*"
+              },
+              "dependencies": {
+                "bignumber.js": {
+                  "version": "git+https://github.com/frozeman/bignumber.js-nolookahead.git#57692b3ecfc98bbdd6b3a516cb2353652ea49934",
+                  "from": "git+https://github.com/frozeman/bignumber.js-nolookahead.git",
+                  "dev": true
+                }
               }
             }
           }