diff --git a/packages/protocol/contracts/layer2/core/Anchor.sol b/packages/protocol/contracts/layer2/core/Anchor.sol
index 1f1b1cc6e6..606d3aa7ea 100644
--- a/packages/protocol/contracts/layer2/core/Anchor.sol
+++ b/packages/protocol/contracts/layer2/core/Anchor.sol
@@ -47,10 +47,14 @@ contract Anchor is EssentialContract {
     }
 
     /// @notice Metadata that will be required for slashing violations of permissionless preconfs.
+    /// @dev `stored` marks an existing entry so callers can distinguish a recorded block whose
+    /// `anchorBlockNumber` is 0 (a valid "skip checkpoint" value) from a block that was never
+    /// recorded. It packs into the same slot as the preceding `uint48` fields.
     struct PreconfMetadata {
         uint48 anchorBlockNumber;
         uint48 submissionWindowEnd;
         uint48 parentSubmissionWindowEnd;
+        bool stored;
         bytes32 rawTxListHash;
         bytes32 parentRawTxListHash;
     }
@@ -205,7 +209,7 @@ contract Anchor is EssentialContract {
         returns (PreconfMetadata memory)
     {
         PreconfMetadata memory preconfMetadata = _preconfMetadata[_blockNumber];
-        require(preconfMetadata.anchorBlockNumber != 0, InvalidBlockNumber());
+        require(preconfMetadata.stored, InvalidBlockNumber());
         return preconfMetadata;
     }
 
@@ -251,6 +255,7 @@ contract Anchor is EssentialContract {
             anchorBlockNumber: _blockParams.anchorBlockNumber,
             submissionWindowEnd: _proposalParams.submissionWindowEnd,
             parentSubmissionWindowEnd: parentPreconfMetadata.submissionWindowEnd,
+            stored: true,
             rawTxListHash: _blockParams.rawTxListHash,
             parentRawTxListHash: parentPreconfMetadata.rawTxListHash
         });
diff --git a/packages/protocol/test/layer2/core/Anchor.t.sol b/packages/protocol/test/layer2/core/Anchor.t.sol
index f698201e83..bd250c9df0 100644
--- a/packages/protocol/test/layer2/core/Anchor.t.sol
+++ b/packages/protocol/test/layer2/core/Anchor.t.sol
@@ -105,6 +105,30 @@ contract AnchorTest is Test {
         assertEq(checkpointStore.getCheckpoint(staleBlockParams.anchorBlockNumber).blockNumber, 0);
     }
 
+    function test_getPreconfMetadata_recordsBlockAnchoredAtZero() external {
+        // A block may legitimately be anchored with `anchorBlockNumber == 0` ("skip checkpoint").
+        // Its preconf metadata must still be retrievable so the slasher can validate faults; the
+        // `stored` marker distinguishes it from a block that was never recorded.
+        Anchor.ProposalParams memory proposalParams =
+            Anchor.ProposalParams({ submissionWindowEnd: 7 });
+        Anchor.BlockParams memory blockParams = _blockParams(0, 0x1234, 0x5678);
+
+        vm.roll(SHASTA_FORK_HEIGHT);
+        vm.prank(GOLDEN_TOUCH);
+        anchor.anchorV4(proposalParams, blockParams);
+
+        Anchor.PreconfMetadata memory meta = anchor.getPreconfMetadata(block.number);
+        assertTrue(meta.stored);
+        assertEq(meta.anchorBlockNumber, 0);
+        assertEq(meta.submissionWindowEnd, 7);
+    }
+
+    function test_getPreconfMetadata_RevertWhen_BlockNotRecorded() external {
+        vm.roll(SHASTA_FORK_HEIGHT);
+        vm.expectRevert(Anchor.InvalidBlockNumber.selector);
+        anchor.getPreconfMetadata(SHASTA_FORK_HEIGHT + 999);
+    }
+
     // ---------------------------------------------------------------
     // Helpers
     // ---------------------------------------------------------------