diff --git a/src/mocks/PendingBlkTimeAndNrAdvanceCheck.sol b/src/mocks/PendingBlkTimeAndNrAdvanceCheck.sol
index 423175ba..0676845a 100644
--- a/src/mocks/PendingBlkTimeAndNrAdvanceCheck.sol
+++ b/src/mocks/PendingBlkTimeAndNrAdvanceCheck.sol
@@ -9,14 +9,21 @@ import "../precompiles/ArbSys.sol";
 contract PendingBlkTimeAndNrAdvanceCheck {
     uint256 immutable deployedAt;
     uint256 immutable deployedAtBlock;
+    ArbSys constant ARB_SYS = ArbSys(address(100));
 
     constructor() {
         deployedAt = block.timestamp;
-        deployedAtBlock = ArbSys(address(100)).arbBlockNumber();
+        deployedAtBlock = ARB_SYS.arbBlockNumber();
     }
 
     function isAdvancing() external {
         require(block.timestamp > deployedAt, "Time didn't advance");
-        require(ArbSys(address(100)).arbBlockNumber() > deployedAtBlock, "Block didn't advance");
+        require(ARB_SYS.arbBlockNumber() > deployedAtBlock, "Block didn't advance");
+    }
+
+    function checkArbBlockHashReturnsLatest(bytes32 expected) external {
+        bytes32 gotBlockHash = ARB_SYS.arbBlockHash(ARB_SYS.arbBlockNumber() - 1);
+        require(gotBlockHash != bytes32(0), "ZERO_BLOCK_HASH");
+        require(gotBlockHash == expected, "WRONG_BLOCK_HASH");
     }
 }