diff --git a/contracts/GSN/GSNRecipientERC20Fee.sol b/contracts/GSN/GSNRecipientERC20Fee.sol
index ad5dee054..adba27421 100644
--- a/contracts/GSN/GSNRecipientERC20Fee.sol
+++ b/contracts/GSN/GSNRecipientERC20Fee.sol
@@ -86,6 +86,8 @@ contract GSNRecipientERC20Fee is GSNRecipient {
 
         // The maximum token charge is pre-charged from the user
         _token.safeTransferFrom(from, address(this), maxPossibleCharge);
+
+        return 0;
     }
 
     /**
diff --git a/contracts/introspection/IERC1820Registry.sol b/contracts/introspection/IERC1820Registry.sol
index cd9bd5b4e..cc163f6e3 100644
--- a/contracts/introspection/IERC1820Registry.sol
+++ b/contracts/introspection/IERC1820Registry.sol
@@ -59,7 +59,7 @@ interface IERC1820Registry {
      * queried for support, unless `implementer` is the caller. See
      * {IERC1820Implementer-canImplementInterfaceForAddress}.
      */
-    function setInterfaceImplementer(address account, bytes32 interfaceHash, address implementer) external;
+    function setInterfaceImplementer(address account, bytes32 _interfaceHash, address implementer) external;
 
     /**
      * @dev Returns the implementer of `interfaceHash` for `account`. If no such
@@ -70,7 +70,7 @@ interface IERC1820Registry {
      *
      * `account` being the zero address is an alias for the caller's address.
      */
-    function getInterfaceImplementer(address account, bytes32 interfaceHash) external view returns (address);
+    function getInterfaceImplementer(address account, bytes32 _interfaceHash) external view returns (address);
 
     /**
      * @dev Returns the interface hash for an `interfaceName`, as defined in the
diff --git a/contracts/mocks/GSNRecipientMock.sol b/contracts/mocks/GSNRecipientMock.sol
index fc07b61c7..13065c5d7 100644
--- a/contracts/mocks/GSNRecipientMock.sol
+++ b/contracts/mocks/GSNRecipientMock.sol
@@ -13,7 +13,7 @@ contract GSNRecipientMock is ContextMock, GSNRecipient {
 
     function acceptRelayedCall(address, address, bytes calldata, uint256, uint256, uint256, uint256, bytes calldata, uint256)
         external
-        view
+        pure
         override
         returns (uint256, bytes memory)
     {
diff --git a/contracts/payment/PaymentSplitter.sol b/contracts/payment/PaymentSplitter.sol
index e23df3530..fb05cb9a6 100644
--- a/contracts/payment/PaymentSplitter.sol
+++ b/contracts/payment/PaymentSplitter.sol
@@ -39,13 +39,13 @@ contract PaymentSplitter is Context {
      * All addresses in `payees` must be non-zero. Both arrays must have the same non-zero length, and there must be no
      * duplicates in `payees`.
      */
-    constructor (address[] memory payees, uint256[] memory shares) payable {
+    constructor (address[] memory payees, uint256[] memory shares_) payable {
         // solhint-disable-next-line max-line-length
-        require(payees.length == shares.length, "PaymentSplitter: payees and shares length mismatch");
+        require(payees.length == shares_.length, "PaymentSplitter: payees and shares length mismatch");
         require(payees.length > 0, "PaymentSplitter: no payees");
 
         for (uint256 i = 0; i < payees.length; i++) {
-            _addPayee(payees[i], shares[i]);
+            _addPayee(payees[i], shares_[i]);
         }
     }
 
diff --git a/contracts/payment/escrow/RefundEscrow.sol b/contracts/payment/escrow/RefundEscrow.sol
index 071084231..a0bd53be0 100644
--- a/contracts/payment/escrow/RefundEscrow.sol
+++ b/contracts/payment/escrow/RefundEscrow.sol
@@ -25,11 +25,11 @@ contract RefundEscrow is ConditionalEscrow {
 
     /**
      * @dev Constructor.
-     * @param beneficiary The beneficiary of the deposits.
+     * @param beneficiary_ The beneficiary of the deposits.
      */
-    constructor (address payable beneficiary) {
-        require(beneficiary != address(0), "RefundEscrow: beneficiary is the zero address");
-        _beneficiary = beneficiary;
+    constructor (address payable beneficiary_) {
+        require(beneficiary_ != address(0), "RefundEscrow: beneficiary is the zero address");
+        _beneficiary = beneficiary_;
         _state = State.Active;
     }
 
diff --git a/contracts/proxy/TransparentUpgradeableProxy.sol b/contracts/proxy/TransparentUpgradeableProxy.sol
index fc12ebf56..247571b05 100644
--- a/contracts/proxy/TransparentUpgradeableProxy.sol
+++ b/contracts/proxy/TransparentUpgradeableProxy.sol
@@ -30,9 +30,9 @@ contract TransparentUpgradeableProxy is UpgradeableProxy {
      * @dev Initializes an upgradeable proxy managed by `_admin`, backed by the implementation at `_logic`, and
      * optionally initialized with `_data` as explained in {UpgradeableProxy-constructor}.
      */
-    constructor(address _logic, address _admin, bytes memory _data) payable UpgradeableProxy(_logic, _data) {
+    constructor(address _logic, address admin_, bytes memory _data) payable UpgradeableProxy(_logic, _data) {
         assert(_ADMIN_SLOT == bytes32(uint256(keccak256("eip1967.proxy.admin")) - 1));
-        _setAdmin(_admin);
+        _setAdmin(admin_);
     }
 
     /**
@@ -67,8 +67,8 @@ contract TransparentUpgradeableProxy is UpgradeableProxy {
      * https://eth.wiki/json-rpc/API#eth_getstorageat[`eth_getStorageAt`] RPC call.
      * `0xb53127684a568b3173ae13b9f8a6016e243e63b6e8ee1178d6a717850b5d6103`
      */
-    function admin() external ifAdmin returns (address) {
-        return _admin();
+    function admin() external ifAdmin returns (address admin_) {
+        admin_ = _admin();
     }
 
     /**
@@ -80,8 +80,8 @@ contract TransparentUpgradeableProxy is UpgradeableProxy {
      * https://eth.wiki/json-rpc/API#eth_getstorageat[`eth_getStorageAt`] RPC call.
      * `0x360894a13ba1a3210667c828492db98dca3e2076cc3735a920a3ca505d382bbc`
      */
-    function implementation() external ifAdmin returns (address) {
-        return _implementation();
+    function implementation() external ifAdmin returns (address implementation_) {
+        implementation_ = _implementation();
     }
 
     /**
diff --git a/contracts/token/ERC1155/ERC1155.sol b/contracts/token/ERC1155/ERC1155.sol
index b17d7939c..1ecc394a6 100644
--- a/contracts/token/ERC1155/ERC1155.sol
+++ b/contracts/token/ERC1155/ERC1155.sol
@@ -52,8 +52,8 @@ contract ERC1155 is Context, ERC165, IERC1155, IERC1155MetadataURI {
     /**
      * @dev See {_setURI}.
      */
-    constructor (string memory uri) {
-        _setURI(uri);
+    constructor (string memory uri_) {
+        _setURI(uri_);
 
         // register the supported interfaces to conform to ERC1155 via ERC165
         _registerInterface(_INTERFACE_ID_ERC1155);
diff --git a/contracts/token/ERC20/ERC20.sol b/contracts/token/ERC20/ERC20.sol
index 3b9ad9388..35b897137 100644
--- a/contracts/token/ERC20/ERC20.sol
+++ b/contracts/token/ERC20/ERC20.sol
@@ -54,9 +54,9 @@ contract ERC20 is Context, IERC20 {
      * All three of these values are immutable: they can only be set once during
      * construction.
      */
-    constructor (string memory name, string memory symbol) {
-        _name = name;
-        _symbol = symbol;
+    constructor (string memory name_, string memory symbol_) {
+        _name = name_;
+        _symbol = symbol_;
         _decimals = 18;
     }
 
diff --git a/contracts/token/ERC20/ERC20Capped.sol b/contracts/token/ERC20/ERC20Capped.sol
index 0dae5ae74..dc7797025 100644
--- a/contracts/token/ERC20/ERC20Capped.sol
+++ b/contracts/token/ERC20/ERC20Capped.sol
@@ -16,9 +16,9 @@ abstract contract ERC20Capped is ERC20 {
      * @dev Sets the value of the `cap`. This value is immutable, it can only be
      * set once during construction.
      */
-    constructor (uint256 cap) {
-        require(cap > 0, "ERC20Capped: cap is 0");
-        _cap = cap;
+    constructor (uint256 cap_) {
+        require(cap_ > 0, "ERC20Capped: cap is 0");
+        _cap = cap_;
     }
 
     /**
diff --git a/contracts/token/ERC20/TokenTimelock.sol b/contracts/token/ERC20/TokenTimelock.sol
index cecaff579..42d29e0ce 100644
--- a/contracts/token/ERC20/TokenTimelock.sol
+++ b/contracts/token/ERC20/TokenTimelock.sol
@@ -23,12 +23,12 @@ contract TokenTimelock {
     // timestamp when token release is enabled
     uint256 private _releaseTime;
 
-    constructor (IERC20 token, address beneficiary, uint256 releaseTime) {
+    constructor (IERC20 token_, address beneficiary_, uint256 releaseTime_) {
         // solhint-disable-next-line not-rely-on-time
-        require(releaseTime > block.timestamp, "TokenTimelock: release time is before current time");
-        _token = token;
-        _beneficiary = beneficiary;
-        _releaseTime = releaseTime;
+        require(releaseTime_ > block.timestamp, "TokenTimelock: release time is before current time");
+        _token = token_;
+        _beneficiary = beneficiary_;
+        _releaseTime = releaseTime_;
     }
 
     /**
diff --git a/contracts/token/ERC721/ERC721.sol b/contracts/token/ERC721/ERC721.sol
index ada2baf24..cd84ac715 100644
--- a/contracts/token/ERC721/ERC721.sol
+++ b/contracts/token/ERC721/ERC721.sol
@@ -90,9 +90,9 @@ contract ERC721 is Context, ERC165, IERC721, IERC721Metadata, IERC721Enumerable
     /**
      * @dev Initializes the contract by setting a `name` and a `symbol` to the token collection.
      */
-    constructor (string memory name, string memory symbol) {
-        _name = name;
-        _symbol = symbol;
+    constructor (string memory name_, string memory symbol_) {
+        _name = name_;
+        _symbol = symbol_;
 
         // register the supported interfaces to conform to ERC721 via ERC165
         _registerInterface(_INTERFACE_ID_ERC721);
diff --git a/contracts/token/ERC777/ERC777.sol b/contracts/token/ERC777/ERC777.sol
index a781c2e97..38d271ed4 100644
--- a/contracts/token/ERC777/ERC777.sol
+++ b/contracts/token/ERC777/ERC777.sol
@@ -67,14 +67,14 @@ contract ERC777 is Context, IERC777, IERC20 {
      * @dev `defaultOperators` may be an empty array.
      */
     constructor(
-        string memory name,
-        string memory symbol,
-        address[] memory defaultOperators
+        string memory name_,
+        string memory symbol_,
+        address[] memory defaultOperators_
     ) {
-        _name = name;
-        _symbol = symbol;
+        _name = name_;
+        _symbol = symbol_;
 
-        _defaultOperatorsArray = defaultOperators;
+        _defaultOperatorsArray = defaultOperators_;
         for (uint256 i = 0; i < _defaultOperatorsArray.length; i++) {
             _defaultOperators[_defaultOperatorsArray[i]] = true;
         }