diff --git a/packages/testing/src/consensus_testing/test_fixtures/verify_signatures.py b/packages/testing/src/consensus_testing/test_fixtures/verify_signatures.py
index 77fd9e86..11be0ec5 100644
--- a/packages/testing/src/consensus_testing/test_fixtures/verify_signatures.py
+++ b/packages/testing/src/consensus_testing/test_fixtures/verify_signatures.py
@@ -6,6 +6,7 @@
 
 from pydantic import Field
 
+from lean_spec.spec.crypto.merkleization import hash_tree_root
 from lean_spec.spec.forks import AggregationBits, Checkpoint, Slot, ValidatorIndex
 from lean_spec.spec.forks.lstar.containers import (
     AggregatedAttestation,
@@ -77,6 +78,9 @@ class VerifySignaturesTest(BaseConsensusFixture):
       signing so the block root differs. Exercises the per-component
       message binding that prevents reusing an honest proof under a
       different message.
+    - `{"operation": "swap_first_two_attestations"}`: Swap the first
+      two body attestations and re-sign only the proposer. Exercises
+      body/proof ordering without relying on a block-root mismatch.
 
     Tampered blocks bypass the builder's structural invariants. The
     resulting fixture pins the exact rejection a client must raise when
@@ -214,4 +218,45 @@ def _apply_tamper(self, signed_block: SignedBlock) -> SignedBlock:
             signed_block.block.state_root = Bytes32(b"\xff" * 32)
             return signed_block
 
+        if operation == "swap_first_two_attestations":
+            body = signed_block.block.body
+            original = body.attestations.data
+            if len(original) < 2:
+                raise ValueError("swap_first_two_attestations requires at least two attestations")
+            assert self.anchor_state is not None
+
+            key_manager = XmssKeyManager.shared()
+            original_attestation_proofs = [
+                key_manager.sign_and_aggregate(
+                    list(attestation.aggregation_bits.to_validator_indices()),
+                    attestation.data,
+                )
+                for attestation in original
+            ]
+
+            swapped_body = body.model_copy(
+                update={
+                    "attestations": AggregatedAttestations(
+                        data=[original[1], original[0], *original[2:]]
+                    )
+                }
+            )
+            swapped_block = signed_block.block.model_copy(update={"body": swapped_body})
+
+            # Keep the block root honestly signed; only the attestation
+            # proof order remains mismatched with the body order.
+            post_state = LstarSpec().process_slots(self.anchor_state, swapped_block.slot)
+            post_state = LstarSpec().process_block(post_state, swapped_block)
+            swapped_block = swapped_block.model_copy(
+                update={"state_root": hash_tree_root(post_state)}
+            )
+
+            return self.block._sign_block(
+                swapped_block,
+                original_attestation_proofs,
+                swapped_block.proposer_index,
+                key_manager,
+                self.anchor_state,
+            )
+
         raise ValueError(f"Unknown tamper operation: {operation!r}")
diff --git a/tests/consensus/lstar/verify_signatures/test_structural_rejections.py b/tests/consensus/lstar/verify_signatures/test_structural_rejections.py
index 76a80efc..e847ae00 100644
--- a/tests/consensus/lstar/verify_signatures/test_structural_rejections.py
+++ b/tests/consensus/lstar/verify_signatures/test_structural_rejections.py
@@ -10,12 +10,15 @@
 
 import pytest
 from consensus_testing import (
+    AggregatedAttestationSpec,
     BlockSpec,
     VerifySignaturesTestFiller,
+    build_anchor,
     generate_pre_state,
 )
 
-from lean_spec.spec.forks import Slot
+from lean_spec.spec.crypto.merkleization import hash_tree_root
+from lean_spec.spec.forks import Slot, ValidatorIndex
 
 pytestmark = pytest.mark.valid_until("Lstar")
 
@@ -115,3 +118,39 @@ def test_proof_reused_under_different_message_rejected(
         tamper={"operation": "mutate_state_root"},
         expect_exception=AssertionError,
     )
+
+
+def test_attestation_proof_order_mismatch_rejected(
+    verify_signatures_test: VerifySignaturesTestFiller,
+) -> None:
+    """A block whose body order no longer matches proof order is rejected."""
+    anchor_state, anchor_block = build_anchor(num_validators=4, anchor_slot=Slot(2))
+    parent_root = hash_tree_root(anchor_block)
+
+    verify_signatures_test(
+        anchor_state=anchor_state,
+        block=BlockSpec(
+            slot=Slot(3),
+            parent_root=parent_root,
+            attestations=[
+                AggregatedAttestationSpec(
+                    validator_indices=[ValidatorIndex(0)],
+                    slot=Slot(3),
+                    target_slot=Slot(1),
+                    target_root=anchor_state.historical_block_hashes[1],
+                    head_root=parent_root,
+                    head_slot=Slot(2),
+                ),
+                AggregatedAttestationSpec(
+                    validator_indices=[ValidatorIndex(2)],
+                    slot=Slot(3),
+                    target_slot=Slot(2),
+                    target_root=parent_root,
+                    head_root=parent_root,
+                    head_slot=Slot(2),
+                ),
+            ],
+        ),
+        tamper={"operation": "swap_first_two_attestations"},
+        expect_exception=AssertionError,
+    )