diff --git a/specs/gloas/fork-choice.md b/specs/gloas/fork-choice.md
index 7bd3d4279db..7a71ac236a9 100644
--- a/specs/gloas/fork-choice.md
+++ b/specs/gloas/fork-choice.md
@@ -486,6 +486,10 @@ def should_apply_proposer_boost(store: Store) -> bool:
     if store.proposer_boost_root == Root():
         return False
 
+    # Withhold boost if the boosted block's proposer has equivocated
+    if is_proposer_equivocation(store, store.proposer_boost_root):
+        return False
+
     block = store.blocks[store.proposer_boost_root]
     parent_root = block.parent_root
     parent = store.blocks[parent_root]
diff --git a/specs/gloas/p2p-interface.md b/specs/gloas/p2p-interface.md
index f55ae7d499a..0efeb4983f2 100644
--- a/specs/gloas/p2p-interface.md
+++ b/specs/gloas/p2p-interface.md
@@ -563,7 +563,9 @@ def validate_beacon_block_gossip(
     if block.slot <= finalized_slot:
         raise GossipIgnore("block is not from a slot greater than the latest finalized slot")
 
-    # [IGNORE] The block is the first block with valid signature received for the slot and proposer
+    # [IGNORE] The block is the first block with valid signature received for the slot and proposer.
+    # Note: Implementations SHOULD still pass this block to `on_block` so both blocks enter
+    # `store.blocks` and `is_proposer_equivocation()` can observe the equivocation.
     proposer_slot_key = (block.slot, block.proposer_index)
     if proposer_slot_key in seen.proposer_slots:
         raise GossipIgnore("block is not the first valid block for this slot and proposer")
diff --git a/specs/phase0/p2p-interface.md b/specs/phase0/p2p-interface.md
index ff2dfb1e640..fbb3e9afe96 100644
--- a/specs/phase0/p2p-interface.md
+++ b/specs/phase0/p2p-interface.md
@@ -636,7 +636,9 @@ def validate_beacon_block_gossip(
     if block.slot <= finalized_slot:
         raise GossipIgnore("block is not from a slot greater than the latest finalized slot")
 
-    # [IGNORE] The block is the first block with valid signature received for the slot and proposer
+    # [IGNORE] The block is the first block with valid signature received for the slot and proposer.
+    # Note: Implementations SHOULD still pass this block to `on_block` so both blocks enter
+    # `store.blocks` and `is_proposer_equivocation()` can observe the equivocation.
     proposer_slot_key = (block.slot, block.proposer_index)
     if proposer_slot_key in seen.proposer_slots:
         raise GossipIgnore("block is not the first valid block for this slot and proposer")
diff --git a/tests/core/pyspec/eth_consensus_specs/test/gloas/fork_choice/test_should_apply_proposer_boost.py b/tests/core/pyspec/eth_consensus_specs/test/gloas/fork_choice/test_should_apply_proposer_boost.py
index 739bf4a5004..1eb3c06d4aa 100644
--- a/tests/core/pyspec/eth_consensus_specs/test/gloas/fork_choice/test_should_apply_proposer_boost.py
+++ b/tests/core/pyspec/eth_consensus_specs/test/gloas/fork_choice/test_should_apply_proposer_boost.py
@@ -234,3 +234,52 @@ def test_should_apply_proposer_boost_withheld(spec, state):
 
     output_store_checks(spec, store, test_steps, with_viable_for_head_weights=True)
     yield "steps", test_steps
+
+
+@with_gloas_and_later
+@with_presets([MINIMAL], reason="too slow")
+@spec_state_test
+def test_should_apply_proposer_boost_proposer_equivocation(spec, state):
+    """
+    The boosted block's own proposer equivocated: a second block from the same
+    proposer at the boosted block's slot. Boost is withheld regardless of the
+    parent-adjacency and weakness conditions checked later in the function. Here the
+    parent is two slots back, so absent the equivocation the "not adjacent" escape
+    would apply the boost; the equivocation overrides it.
+    """
+    store, state, test_steps = yield from setup_finalized_store(spec, state)
+
+    # Leave a gap so the boosted block's parent is two slots back (non-adjacent),
+    # which on its own would make should_apply_proposer_boost return True.
+    next_slot(spec, state)
+
+    pre_state = state.copy()
+    block = build_empty_block_for_next_slot(spec, state)
+    signed_block = state_transition_and_sign_block(spec, state, block)
+    block_root = signed_block.message.hash_tree_root()
+    yield from tick_and_add_block(spec, store, signed_block, test_steps)
+    assert store.proposer_boost_root == block_root
+    # The boosted block's parent is two slots back (empty slot from next_slot above).
+    assert store.blocks[block.parent_root].slot + 2 == block.slot
+
+    # Baseline: without an equivocation, the boost applies (non-adjacent escape).
+    assert spec.should_apply_proposer_boost(store) is True
+    _assert_weight_reflects_boost(spec, store, block_root, boost_applied=True)
+
+    # Build a same-slot same-proposer equivocation of the boosted block.
+    equivocation_state = pre_state.copy()
+    equivocation_block = build_empty_block(spec, equivocation_state, slot=block.slot)
+    equivocation_block.body.graffiti = spec.Bytes32(b"\x01" * 32)
+    signed_equivocation = state_transition_and_sign_block(
+        spec, equivocation_state, equivocation_block
+    )
+    assert signed_equivocation.message.proposer_index == signed_block.message.proposer_index
+    assert signed_equivocation.message.hash_tree_root() != block_root
+    yield from add_block(spec, store, signed_equivocation, test_steps)
+
+    # The boosted block's proposer has now equivocated -> boost is withheld.
+    assert spec.should_apply_proposer_boost(store) is False
+    _assert_weight_reflects_boost(spec, store, block_root, boost_applied=False)
+
+    output_store_checks(spec, store, test_steps, with_viable_for_head_weights=True)
+    yield "steps", test_steps