diff --git a/contracts/access/roles/WhitelistAdminRole.sol b/contracts/access/roles/WhitelistAdminRole.sol
index e8bc0ab48..cebb50356 100644
--- a/contracts/access/roles/WhitelistAdminRole.sol
+++ b/contracts/access/roles/WhitelistAdminRole.sol
@@ -48,4 +48,6 @@ contract WhitelistAdminRole is Initializable {
         _whitelistAdmins.remove(account);
         emit WhitelistAdminRemoved(account);
     }
+
+    uint256[50] private ______gap;
 }
diff --git a/contracts/access/roles/WhitelistedRole.sol b/contracts/access/roles/WhitelistedRole.sol
index 87b146b95..69687e858 100644
--- a/contracts/access/roles/WhitelistedRole.sol
+++ b/contracts/access/roles/WhitelistedRole.sol
@@ -53,4 +53,7 @@ contract WhitelistedRole is Initializable, WhitelistAdminRole {
         _whitelisteds.remove(account);
         emit WhitelistedRemoved(account);
     }
+
+    uint256[50] private ______gap;
+}
 }
diff --git a/contracts/crowdsale/distribution/RefundablePostDeliveryCrowdsale.sol b/contracts/crowdsale/distribution/RefundablePostDeliveryCrowdsale.sol
index be4c5b6a0..256109684 100644
--- a/contracts/crowdsale/distribution/RefundablePostDeliveryCrowdsale.sol
+++ b/contracts/crowdsale/distribution/RefundablePostDeliveryCrowdsale.sol
@@ -1,20 +1,23 @@
 pragma solidity ^0.5.0;
 
+import "zos-lib/contracts/Initializable.sol";
+
 import "./RefundableCrowdsale.sol";
 import "./PostDeliveryCrowdsale.sol";
 
-
 /**
  * @title RefundablePostDeliveryCrowdsale
  * @dev Extension of RefundableCrowdsale contract that only delivers the tokens
  * once the crowdsale has closed and the goal met, preventing refunds to be issued
  * to token holders.
  */
-contract RefundablePostDeliveryCrowdsale is RefundableCrowdsale, PostDeliveryCrowdsale {
+contract RefundablePostDeliveryCrowdsale is Initializable, RefundableCrowdsale, PostDeliveryCrowdsale {
     function withdrawTokens(address beneficiary) public {
         require(finalized());
         require(goalReached());
 
         super.withdrawTokens(beneficiary);
     }
+
+    uint256[50] private ______gap;
 }
diff --git a/contracts/crowdsale/validation/PausableCrowdsale.sol b/contracts/crowdsale/validation/PausableCrowdsale.sol
index a5f3ac584..9ff89059f 100644
--- a/contracts/crowdsale/validation/PausableCrowdsale.sol
+++ b/contracts/crowdsale/validation/PausableCrowdsale.sol
@@ -26,4 +26,6 @@ contract PausableCrowdsale is Initializable, Crowdsale, Pausable {
     function _preValidatePurchase(address _beneficiary, uint256 _weiAmount) internal view whenNotPaused {
         return super._preValidatePurchase(_beneficiary, _weiAmount);
     }
+
+    uint256[50] private ______gap;
 }
diff --git a/contracts/crowdsale/validation/WhitelistCrowdsale.sol b/contracts/crowdsale/validation/WhitelistCrowdsale.sol
index 29e13b617..213d62d39 100644
--- a/contracts/crowdsale/validation/WhitelistCrowdsale.sol
+++ b/contracts/crowdsale/validation/WhitelistCrowdsale.sol
@@ -10,6 +10,8 @@ import "../../access/roles/WhitelistedRole.sol";
 contract WhitelistCrowdsale is Initializable, WhitelistedRole, Crowdsale {
     function initialize(address sender) public initializer {
         WhitelistedRole._initialize(sender);
+
+        assert(Crowdsale._hasBeenInitialized());
     }
 
     /**
@@ -22,4 +24,6 @@ contract WhitelistCrowdsale is Initializable, WhitelistedRole, Crowdsale {
         require(isWhitelisted(_beneficiary));
         super._preValidatePurchase(_beneficiary, _weiAmount);
     }
+
+    uint256[50] private ______gap;
 }
diff --git a/contracts/payment/PaymentSplitter.sol b/contracts/payment/PaymentSplitter.sol
index 82b768ec1..21211d626 100644
--- a/contracts/payment/PaymentSplitter.sol
+++ b/contracts/payment/PaymentSplitter.sol
@@ -111,4 +111,6 @@ contract PaymentSplitter is Initializable {
         _totalShares = _totalShares.add(shares_);
         emit PayeeAdded(account, shares_);
     }
+
+    uint256[50] private ______gap;
 }
diff --git a/contracts/payment/escrow/ConditionalEscrow.sol b/contracts/payment/escrow/ConditionalEscrow.sol
index 283d59d60..4128adde6 100644
--- a/contracts/payment/escrow/ConditionalEscrow.sol
+++ b/contracts/payment/escrow/ConditionalEscrow.sol
@@ -23,4 +23,6 @@ contract ConditionalEscrow is Initializable, Escrow {
         require(withdrawalAllowed(payee));
         super.withdraw(payee);
     }
+
+    uint256[50] private ______gap;
 }
diff --git a/contracts/payment/escrow/Escrow.sol b/contracts/payment/escrow/Escrow.sol
index 5ff736cec..8325b493f 100644
--- a/contracts/payment/escrow/Escrow.sol
+++ b/contracts/payment/escrow/Escrow.sol
@@ -55,4 +55,6 @@ contract Escrow is Initializable, Secondary {
 
         emit Withdrawn(payee, payment);
     }
+
+    uint256[50] private ______gap;
 }
diff --git a/contracts/payment/escrow/RefundEscrow.sol b/contracts/payment/escrow/RefundEscrow.sol
index ac67f8cc3..fc146479b 100644
--- a/contracts/payment/escrow/RefundEscrow.sol
+++ b/contracts/payment/escrow/RefundEscrow.sol
@@ -93,4 +93,6 @@ contract RefundEscrow is Initializable, ConditionalEscrow {
     function withdrawalAllowed(address) public view returns (bool) {
         return _state == State.Refunding;
     }
+
+    uint256[50] private ______gap;
 }
diff --git a/contracts/token/ERC20/ERC20Pausable.sol b/contracts/token/ERC20/ERC20Pausable.sol
index 0c6d8ee1d..657fcabcf 100644
--- a/contracts/token/ERC20/ERC20Pausable.sol
+++ b/contracts/token/ERC20/ERC20Pausable.sol
@@ -32,4 +32,6 @@ contract ERC20Pausable is Initializable, ERC20, Pausable {
     function decreaseAllowance(address spender, uint subtractedValue) public whenNotPaused returns (bool success) {
         return super.decreaseAllowance(spender, subtractedValue);
     }
+
+    uint256[50] private ______gap;
 }
diff --git a/contracts/token/ERC20/StandaloneERC20.sol b/contracts/token/ERC20/StandaloneERC20.sol
index 9d5e6cedc..4c07ade54 100644
--- a/contracts/token/ERC20/StandaloneERC20.sol
+++ b/contracts/token/ERC20/StandaloneERC20.sol
@@ -60,4 +60,6 @@ contract StandaloneERC20 is Initializable, ERC20Detailed, ERC20Mintable, ERC20Pa
             _addPauser(pausers[i]);
         }
     }
+
+    uint256[50] private ______gap;
 }