diff --git a/solidity/app/hardhat.config.ts b/solidity/app/hardhat.config.ts
index f5c2b6cd5..f4fbb2824 100644
--- a/solidity/app/hardhat.config.ts
+++ b/solidity/app/hardhat.config.ts
@@ -10,7 +10,7 @@ module.exports = {
   solidity: {
     compilers: [
       {
-        version: '0.8.13',
+        version: '0.8.16',
       },
       {
         version: '0.7.6',
diff --git a/solidity/core/contracts/Inbox.sol b/solidity/core/contracts/Inbox.sol
index c69fe3525..a19f4231a 100644
--- a/solidity/core/contracts/Inbox.sol
+++ b/solidity/core/contracts/Inbox.sol
@@ -66,7 +66,7 @@ contract Inbox is IInbox, ReentrancyGuardUpgradeable, Versioned, Mailbox {
     // ============ Initializer ============
 
     function initialize(uint32 _remoteDomain, address _validatorManager)
-        public
+        external
         initializer
     {
         __ReentrancyGuard_init();
diff --git a/solidity/core/contracts/Outbox.sol b/solidity/core/contracts/Outbox.sol
index 03550636f..3d87df6ad 100644
--- a/solidity/core/contracts/Outbox.sol
+++ b/solidity/core/contracts/Outbox.sol
@@ -86,7 +86,7 @@ contract Outbox is IOutbox, Versioned, MerkleTreeManager, Mailbox {
 
     // ============ Initializer ============
 
-    function initialize(address _validatorManager) public initializer {
+    function initialize(address _validatorManager) external initializer {
         __Mailbox_initialize(_validatorManager);
         state = States.Active;
     }
diff --git a/solidity/core/hardhat.config.ts b/solidity/core/hardhat.config.ts
index a271dcb4e..c5299cd6e 100644
--- a/solidity/core/hardhat.config.ts
+++ b/solidity/core/hardhat.config.ts
@@ -9,7 +9,7 @@ import 'solidity-coverage';
  */
 module.exports = {
   solidity: {
-    version: '0.8.13',
+    version: '0.8.16',
     settings: {
       optimizer: {
         enabled: true,
diff --git a/typescript/helloworld/hardhat.config.ts b/typescript/helloworld/hardhat.config.ts
index ec91c1574..7c2e51c6f 100644
--- a/typescript/helloworld/hardhat.config.ts
+++ b/typescript/helloworld/hardhat.config.ts
@@ -11,7 +11,7 @@ module.exports = {
   solidity: {
     compilers: [
       {
-        version: '0.8.13',
+        version: '0.8.16',
       },
     ],
   },