diff --git a/packages/protocol/contracts/L1/TaikoData.sol b/packages/protocol/contracts/L1/TaikoData.sol
index e66625c9894..d838b51025e 100644
--- a/packages/protocol/contracts/L1/TaikoData.sol
+++ b/packages/protocol/contracts/L1/TaikoData.sol
@@ -121,6 +121,7 @@ library TaikoData {
         bytes32 blockHash;
         bytes32 stateRoot;
         bytes32 graffiti;
+        bytes32[2] __reserved;
     }
 
     /// @dev Struct representing state transition data.
diff --git a/packages/protocol/contracts/signal/SignalService.sol b/packages/protocol/contracts/signal/SignalService.sol
index 11e8df6c974..3e4253b5146 100644
--- a/packages/protocol/contracts/signal/SignalService.sol
+++ b/packages/protocol/contracts/signal/SignalService.sol
@@ -124,8 +124,7 @@ contract SignalService is EssentialContract, ISignalService {
         // If a signal is sent from chainA -> chainB -> chainC (this chain), we verify the proofs in
         // the following order:
         // 1. using chainC's latest parent's stateRoot to verify that chainB's TaikoL1/TaikoL2
-        // contract has
-        // sent a given hop stateRoot on chainB using its own signal service.
+        // contract has sent a given hop stateRoot on chainB using its own signal service.
         // 2. using the verified hop stateRoot to verify that the source app on chainA has sent a
         // signal using its own signal service.
         // We always verify the proofs in the reversed order (top to bottom).
diff --git a/packages/protocol/test/L1/TaikoL1LibProvingWithTiers.t.sol b/packages/protocol/test/L1/TaikoL1LibProvingWithTiers.t.sol
index a1d35e73d61..bd4e3042cd1 100644
--- a/packages/protocol/test/L1/TaikoL1LibProvingWithTiers.t.sol
+++ b/packages/protocol/test/L1/TaikoL1LibProvingWithTiers.t.sol
@@ -790,7 +790,8 @@ contract TaikoL1LibProvingWithTiers is TaikoL1TestBase {
                     parentHash: parentHash,
                     blockHash: blockHash,
                     stateRoot: stateRoot,
-                    graffiti: 0x0
+                    graffiti: 0x0,
+                    __reserved: [bytes32(0), bytes32(0)]
                 });
 
                 TaikoData.TierProof memory proof;
diff --git a/packages/protocol/test/L1/TaikoL1TestBase.sol b/packages/protocol/test/L1/TaikoL1TestBase.sol
index 14e2c395627..d6c7040056d 100644
--- a/packages/protocol/test/L1/TaikoL1TestBase.sol
+++ b/packages/protocol/test/L1/TaikoL1TestBase.sol
@@ -242,7 +242,8 @@ abstract contract TaikoL1TestBase is TaikoTest {
             parentHash: parentHash,
             blockHash: blockHash,
             stateRoot: stateRoot,
-            graffiti: 0x0
+            graffiti: 0x0,
+            __reserved: [bytes32(0), bytes32(0)]
         });
 
         bytes32 instance =
diff --git a/packages/protocol/test/verifiers/GuardianVerifier.t.sol b/packages/protocol/test/verifiers/GuardianVerifier.t.sol
index 043534e38b3..f47fbea7162 100644
--- a/packages/protocol/test/verifiers/GuardianVerifier.t.sol
+++ b/packages/protocol/test/verifiers/GuardianVerifier.t.sol
@@ -32,7 +32,8 @@ contract TestGuardianVerifier is TaikoL1TestBase {
             parentHash: bytes32(0),
             blockHash: bytes32(0),
             stateRoot: bytes32(0),
-            graffiti: bytes32(0)
+            graffiti: bytes32(0),
+            __reserved: [bytes32(0), bytes32(0)]
         });
 
         // TierProof
@@ -59,7 +60,8 @@ contract TestGuardianVerifier is TaikoL1TestBase {
             parentHash: bytes32(0),
             blockHash: bytes32(0),
             stateRoot: bytes32(0),
-            graffiti: bytes32(0)
+            graffiti: bytes32(0),
+            __reserved: [bytes32(0), bytes32(0)]
         });
 
         // TierProof
diff --git a/packages/protocol/test/verifiers/PseZkVerifier.t.sol b/packages/protocol/test/verifiers/PseZkVerifier.t.sol
index 9225394fd80..03834b1ac47 100644
--- a/packages/protocol/test/verifiers/PseZkVerifier.t.sol
+++ b/packages/protocol/test/verifiers/PseZkVerifier.t.sol
@@ -50,7 +50,8 @@ contract TestPseZkVerifier is TaikoL1TestBase {
             parentHash: bytes32(0),
             blockHash: bytes32(0),
             stateRoot: bytes32(0),
-            graffiti: bytes32(0)
+            graffiti: bytes32(0),
+            __reserved: [bytes32(0), bytes32(0)]
         });
 
         // TierProof
@@ -77,7 +78,8 @@ contract TestPseZkVerifier is TaikoL1TestBase {
             parentHash: bytes32(0),
             blockHash: bytes32(0),
             stateRoot: bytes32(0),
-            graffiti: bytes32(0)
+            graffiti: bytes32(0),
+            __reserved: [bytes32(0), bytes32(0)]
         });
 
         // TierProof
@@ -128,7 +130,8 @@ contract TestPseZkVerifier is TaikoL1TestBase {
             parentHash: bytes32("12"),
             blockHash: bytes32("23"),
             stateRoot: bytes32("34"),
-            graffiti: bytes32("1234")
+            graffiti: bytes32("1234"),
+            __reserved: [bytes32(0), bytes32(0)]
         });
 
         // TierProof
@@ -165,7 +168,8 @@ contract TestPseZkVerifier is TaikoL1TestBase {
             parentHash: bytes32("12"),
             blockHash: bytes32("23"),
             stateRoot: bytes32("34"),
-            graffiti: bytes32("1234")
+            graffiti: bytes32("1234"),
+            __reserved: [bytes32(0), bytes32(0)]
         });
 
         // TierProof
@@ -194,7 +198,8 @@ contract TestPseZkVerifier is TaikoL1TestBase {
             parentHash: bytes32("12"),
             blockHash: bytes32("23"),
             stateRoot: bytes32("34"),
-            graffiti: bytes32("1234")
+            graffiti: bytes32("1234"),
+            __reserved: [bytes32(0), bytes32(0)]
         });
 
         // TierProof
@@ -232,7 +237,8 @@ contract TestPseZkVerifier is TaikoL1TestBase {
             parentHash: bytes32("12"),
             blockHash: bytes32("23"),
             stateRoot: bytes32("34"),
-            graffiti: bytes32("1234")
+            graffiti: bytes32("1234"),
+            __reserved: [bytes32(0), bytes32(0)]
         });
 
         // TierProof
@@ -269,7 +275,8 @@ contract TestPseZkVerifier is TaikoL1TestBase {
             parentHash: bytes32("12"),
             blockHash: bytes32("23"),
             stateRoot: bytes32("34"),
-            graffiti: bytes32("1234")
+            graffiti: bytes32("1234"),
+            __reserved: [bytes32(0), bytes32(0)]
         });
 
         // TierProof
@@ -303,7 +310,8 @@ contract TestPseZkVerifier is TaikoL1TestBase {
             parentHash: bytes32("12"),
             blockHash: bytes32("23"),
             stateRoot: bytes32("34"),
-            graffiti: bytes32("1234")
+            graffiti: bytes32("1234"),
+            __reserved: [bytes32(0), bytes32(0)]
         });
 
         // TierProof
@@ -344,7 +352,8 @@ contract TestPseZkVerifier is TaikoL1TestBase {
             parentHash: bytes32("12"),
             blockHash: bytes32("23"),
             stateRoot: bytes32("34"),
-            graffiti: bytes32("1234")
+            graffiti: bytes32("1234"),
+            __reserved: [bytes32(0), bytes32(0)]
         });
 
         // TierProof
@@ -385,7 +394,8 @@ contract TestPseZkVerifier is TaikoL1TestBase {
             parentHash: bytes32("12"),
             blockHash: bytes32("23"),
             stateRoot: bytes32("34"),
-            graffiti: bytes32("1234")
+            graffiti: bytes32("1234"),
+            __reserved: [bytes32(0), bytes32(0)]
         });
 
         // TierProof
@@ -423,7 +433,8 @@ contract TestPseZkVerifier is TaikoL1TestBase {
             parentHash: bytes32("12"),
             blockHash: bytes32("23"),
             stateRoot: bytes32("34"),
-            graffiti: bytes32("1234")
+            graffiti: bytes32("1234"),
+            __reserved: [bytes32(0), bytes32(0)]
         });
 
         // TierProof
diff --git a/packages/protocol/test/verifiers/SgxVerifier.t.sol b/packages/protocol/test/verifiers/SgxVerifier.t.sol
index 6d125bbcd06..5187eb33254 100644
--- a/packages/protocol/test/verifiers/SgxVerifier.t.sol
+++ b/packages/protocol/test/verifiers/SgxVerifier.t.sol
@@ -195,7 +195,8 @@ contract TestSgxVerifier is TaikoL1TestBase, AttestationBase {
             parentHash: bytes32("12"),
             blockHash: bytes32("34"),
             stateRoot: bytes32("56"),
-            graffiti: bytes32("78")
+            graffiti: bytes32("78"),
+            __reserved: [bytes32(0), bytes32(0)]
         });
 
         // TierProof
@@ -243,7 +244,8 @@ contract TestSgxVerifier is TaikoL1TestBase, AttestationBase {
             parentHash: bytes32("12"),
             blockHash: bytes32("34"),
             stateRoot: bytes32("56"),
-            graffiti: bytes32("78")
+            graffiti: bytes32("78"),
+            __reserved: [bytes32(0), bytes32(0)]
         });
 
         // TierProof
@@ -274,7 +276,8 @@ contract TestSgxVerifier is TaikoL1TestBase, AttestationBase {
             parentHash: bytes32("12"),
             blockHash: bytes32("34"),
             stateRoot: bytes32("56"),
-            graffiti: bytes32("78")
+            graffiti: bytes32("78"),
+            __reserved: [bytes32(0), bytes32(0)]
         });
 
         // TierProof
@@ -307,7 +310,8 @@ contract TestSgxVerifier is TaikoL1TestBase, AttestationBase {
             parentHash: bytes32("12"),
             blockHash: bytes32("34"),
             stateRoot: bytes32("56"),
-            graffiti: bytes32("78")
+            graffiti: bytes32("78"),
+            __reserved: [bytes32(0), bytes32(0)]
         });
 
         // TierProof
@@ -345,7 +349,8 @@ contract TestSgxVerifier is TaikoL1TestBase, AttestationBase {
             parentHash: bytes32("12"),
             blockHash: bytes32("34"),
             stateRoot: bytes32("56"),
-            graffiti: bytes32("78")
+            graffiti: bytes32("78"),
+            __reserved: [bytes32(0), bytes32(0)]
         });
 
         // TierProof
@@ -384,7 +389,8 @@ contract TestSgxVerifier is TaikoL1TestBase, AttestationBase {
             parentHash: bytes32("12"),
             blockHash: bytes32("34"),
             stateRoot: bytes32("56"),
-            graffiti: bytes32("78")
+            graffiti: bytes32("78"),
+            __reserved: [bytes32(0), bytes32(0)]
         });
 
         // TierProof