diff --git a/src/Gateway.sol b/src/Gateway.sol
index 1e59a23..3da6348 100644
--- a/src/Gateway.sol
+++ b/src/Gateway.sol
@@ -70,7 +70,7 @@ contract Gateway is IGateway, IExecutor, IUpgradable, GatewayEIP712 {
     mapping(bytes32 => GmpInfo) private _messages;
 
     // Hash of the previous GMP message submitted.
-    uint256 private _nonce;
+    mapping(address => uint256) private _nonces;
 
     // Replay protection mechanism, stores the hash of the executed messages
     // messageHash => shardId
@@ -92,13 +92,8 @@ contract Gateway is IGateway, IExecutor, IUpgradable, GatewayEIP712 {
     // EIP-712 typed hash
     function initialize(address proxyAdmin, TssKey[] calldata keys, Network[] calldata networks) external {
         require(PROXY_ADDRESS == address(this) || msg.sender == FACTORY, "only proxy can be initialize");
-        require(_nonce == 0, "already initialized");
         ERC1967.setAdmin(proxyAdmin);
 
-        // Initialize the `nonce` as one to avoid the first GMP to spent more gas,
-        // once initialize the storage cost 21k gas, while alter it cost just 2800 gas.
-        _nonce = 1;
-
         // Register networks
         RouteStore.getMainStorage().initialize(networks, NetworkID.wrap(NETWORK_ID));
 
@@ -111,7 +106,7 @@ contract Gateway is IGateway, IExecutor, IUpgradable, GatewayEIP712 {
     }
 
     function nonce() external view returns (uint256) {
-        return _nonce;
+        return _nonces[msg.sender];
     }
 
     function gmpInfo(bytes32 id) external view returns (GmpInfo memory) {
@@ -301,8 +296,8 @@ contract Gateway is IGateway, IExecutor, IUpgradable, GatewayEIP712 {
         // We use 20 bytes for represent the address and 1 bit for the contract flag
         GmpSender source = msg.sender.toSender(false);
 
-        // Salt is equal to the previous message id (EIP-712 hash), this allows us to establish a sequence and eaily query the message history.
-        uint256 nextNonce = _nonce++;
+        // Nonce is per sender, it's incremented for every message sent.
+        uint256 nextNonce = _nonces[msg.sender]++;
 
         // Create GMP message and update nonce
         GmpMessage memory message =
diff --git a/src/utils/GasUtils.sol b/src/utils/GasUtils.sol
index 03bf887..da46e83 100644
--- a/src/utils/GasUtils.sol
+++ b/src/utils/GasUtils.sol
@@ -25,7 +25,12 @@ library GasUtils {
     /**
      * @dev Base cost of the `IGateway.submitMessage` method.
      */
-    uint256 internal constant SUBMIT_BASE_COST = 23449 + 19;
+    uint256 internal constant SUBMIT_BASE_COST = 23525;
+
+    /**
+     * @dev Extra gas cost of the first `IGateway.submitMessage` method.
+     */
+    uint256 internal constant FIRST_MESSAGE_EXTRA_COST = 17100;
 
     /**
      * @dev Compute the gas cost of memory expansion.
diff --git a/test/Example.t.sol b/test/Example.t.sol
index 94c0376..a7de3db 100644
--- a/test/Example.t.sol
+++ b/test/Example.t.sol
@@ -109,7 +109,7 @@ contract ExampleTest is Test {
             dest: address(dstToken),
             destNetwork: DEST_NETWORK_ID,
             gasLimit: 100_000,
-            salt: 1,
+            salt: 0,
             data: abi.encode(MockERC20.CrossChainTransfer({from: ALICE, to: BOB, amount: 100}))
         });
 
diff --git a/test/Gateway.t.sol b/test/Gateway.t.sol
index 135bbba..43d3146 100644
--- a/test/Gateway.t.sol
+++ b/test/Gateway.t.sol
@@ -403,7 +403,7 @@ contract GatewayBase is Test {
 
         assertEq(
             ctx.executionCost,
-            GasUtils.submitMessageGasCost(uint16(gmp.data.length)) - 4500,
+            GasUtils.submitMessageGasCost(uint16(gmp.data.length)) - 4500 + 17100,
             "unexpected submit message gas cost"
         );
     }
@@ -420,7 +420,7 @@ contract GatewayBase is Test {
             dest: address(bytes20(keccak256("dummy_address"))),
             destNetwork: DEST_NETWORK_ID,
             gasLimit: 0,
-            salt: 1,
+            salt: 0,
             data: new bytes(messageSize)
         });
 
@@ -458,12 +458,13 @@ contract GatewayBase is Test {
         emit IGateway.GmpCreated(
             id, GmpSender.unwrap(gmp.source), gmp.dest, gmp.destNetwork, gmp.gasLimit, gmp.salt, gmp.data
         );
+        ctx.gasLimit += 17100;
         assertEq(ctx.submitMessage(gmp), id, "unexpected GMP id");
 
         // Verify the execution cost
         assertEq(
             ctx.executionCost,
-            GasUtils.submitMessageGasCost(uint16(gmp.data.length)),
+            GasUtils.submitMessageGasCost(uint16(gmp.data.length)) + 17100,
             "unexpected submit message gas cost"
         );
 
@@ -622,7 +623,7 @@ contract GatewayBase is Test {
         ctx.execute(sig, gmp);
     }
 
-    function testSubmitGmpMessage() external {
+    function test_submitGmpMessage() external {
         vm.txGasPrice(1);
         GmpSender gmpSender = TestUtils.createTestAccount(1000 ether).toSender(false);
         GmpMessage memory gmp = GmpMessage({
@@ -631,13 +632,13 @@ contract GatewayBase is Test {
             dest: address(receiver),
             destNetwork: DEST_NETWORK_ID,
             gasLimit: 100_000,
-            salt: 1,
+            salt: 0,
             data: abi.encodePacked(uint256(100_000))
         });
         bytes32 id = gmp.eip712hash();
 
         // Check the previous message hash
-        assertEq(gateway.nonce(), 1, "wrong previous message hash");
+        assertEq(gateway.nonce(), 0, "wrong previous message hash");
 
         CallOptions memory ctx = CallOptions({
             from: gmpSender.toAddress(),
@@ -671,8 +672,8 @@ contract GatewayBase is Test {
         assertEq(ctx.submitMessage(gmp), id, "unexpected GMP id");
 
         // Verify the gas cost
-        uint256 expectedCost = GasUtils.submitMessageGasCost(uint16(gmp.data.length)) - 6500;
-        assertEq(ctx.executionCost, expectedCost, "unexpected execution gas cost in first call");
+        uint256 expectedCost = GasUtils.submitMessageGasCost(uint16(gmp.data.length)) - 4500;
+        assertEq(ctx.executionCost, expectedCost + 17100, "unexpected execution gas cost in first call");
 
         // Now the second GMP message should have the salt equals to previous gmp hash
         gmp.salt += 1;
@@ -684,7 +685,7 @@ contract GatewayBase is Test {
             id, GmpSender.unwrap(gmp.source), gmp.dest, gmp.destNetwork, gmp.gasLimit, gmp.salt, gmp.data
         );
         assertEq(ctx.submitMessage(gmp), id, "unexpected GMP id");
-        assertEq(ctx.executionCost, expectedCost - 6800, "unexpected execution gas cost in second call");
+        assertEq(ctx.executionCost, expectedCost - 8800, "unexpected execution gas cost in second call");
     }
 }