diff --git a/packages/beacon-node/src/chain/errors/proposerPreferences.ts b/packages/beacon-node/src/chain/errors/proposerPreferences.ts
index 32804c47f10b..d7be500a858a 100644
--- a/packages/beacon-node/src/chain/errors/proposerPreferences.ts
+++ b/packages/beacon-node/src/chain/errors/proposerPreferences.ts
@@ -5,6 +5,7 @@ export enum ProposerPreferencesErrorCode {
   INVALID_EPOCH = "PROPOSER_PREFERENCES_ERROR_INVALID_EPOCH",
   PROPOSAL_SLOT_PASSED = "PROPOSER_PREFERENCES_ERROR_PROPOSAL_SLOT_PASSED",
   UNKNOWN_DEPENDENT_ROOT = "PROPOSER_PREFERENCES_ERROR_UNKNOWN_DEPENDENT_ROOT",
+  INVALID_DEPENDENT_ROOT = "PROPOSER_PREFERENCES_ERROR_INVALID_DEPENDENT_ROOT",
   INVALID_PROPOSER = "PROPOSER_PREFERENCES_ERROR_INVALID_PROPOSER",
   ALREADY_KNOWN = "PROPOSER_PREFERENCES_ERROR_ALREADY_KNOWN",
   INVALID_SIGNATURE = "PROPOSER_PREFERENCES_ERROR_INVALID_SIGNATURE",
@@ -26,6 +27,11 @@ export type ProposerPreferencesErrorType =
       proposalSlot: Slot;
       dependentRoot: RootHex;
     }
+  | {
+      code: ProposerPreferencesErrorCode.INVALID_DEPENDENT_ROOT;
+      proposalSlot: Slot;
+      dependentRoot: RootHex;
+    }
   | {
       code: ProposerPreferencesErrorCode.INVALID_PROPOSER;
       proposalSlot: Slot;
diff --git a/packages/beacon-node/src/chain/validation/proposerPreferences.ts b/packages/beacon-node/src/chain/validation/proposerPreferences.ts
index 8c2fbe1689ab..43dae26ebb7a 100644
--- a/packages/beacon-node/src/chain/validation/proposerPreferences.ts
+++ b/packages/beacon-node/src/chain/validation/proposerPreferences.ts
@@ -1,6 +1,7 @@
-import {SLOTS_PER_EPOCH} from "@lodestar/params";
+import {GENESIS_SLOT, MIN_SEED_LOOKAHEAD, SLOTS_PER_EPOCH} from "@lodestar/params";
 import {
   computeEpochAtSlot,
+  computeStartSlotAtEpoch,
   createSingleSignatureSetFromComponents,
   getProposerPreferencesSigningRoot,
 } from "@lodestar/state-transition";
@@ -70,6 +71,18 @@ export async function validateGossipProposerPreferences(
     });
   }
 
+  // [REJECT] Dependent block after the lookahead decision slot (clamped to `GENESIS_SLOT` so early epochs
+  // don't underflow). Kept after the proposer-resolution IGNORE so state-unavailable roots stay IGNORE (`ignore_dependent_root_state_unavailable`).
+  const decisionSlot = Math.max(GENESIS_SLOT, computeStartSlotAtEpoch(proposalEpoch - MIN_SEED_LOOKAHEAD) - 1);
+  const dependentBlock = chain.forkChoice.getBlockHexDefaultStatus(dependentRootHex);
+  if (dependentBlock !== null && dependentBlock.slot > decisionSlot) {
+    throw new ProposerPreferencesError(GossipAction.REJECT, {
+      code: ProposerPreferencesErrorCode.INVALID_DEPENDENT_ROOT,
+      proposalSlot,
+      dependentRoot: dependentRootHex,
+    });
+  }
+
   // [REJECT] `is_valid_proposal_slot(state, preferences)` returns True.
   if (proposers[proposalSlot % SLOTS_PER_EPOCH] !== validatorIndex) {
     throw new ProposerPreferencesError(GossipAction.REJECT, {