diff --git a/beacon/engine/errors.go b/beacon/engine/errors.go
index 89a3472084..0bfc289b52 100644
--- a/beacon/engine/errors.go
+++ b/beacon/engine/errors.go
@@ -85,6 +85,7 @@ var (
 	TooLargeRequest          = &EngineAPIError{code: -38004, msg: "Too large request"}
 	InvalidParams            = &EngineAPIError{code: -32602, msg: "Invalid parameters"}
 	UnsupportedFork          = &EngineAPIError{code: -38005, msg: "Unsupported fork"}
+	UnknownParent            = &EngineAPIError{code: -38006, msg: "Unknown parent"}
 
 	STATUS_INVALID         = ForkChoiceResponse{PayloadStatus: PayloadStatusV1{Status: INVALID}, PayloadID: nil}
 	STATUS_SYNCING         = ForkChoiceResponse{PayloadStatus: PayloadStatusV1{Status: SYNCING}, PayloadID: nil}
diff --git a/eth/catalyst/api.go b/eth/catalyst/api.go
index ffa38df2ba..88b9d1562a 100644
--- a/eth/catalyst/api.go
+++ b/eth/catalyst/api.go
@@ -655,6 +655,10 @@ func (api *ConsensusAPI) GetInclusionListV1(parentHash common.Hash) (types.Inclu
 		return inclusionList, nil
 	}
 
+	if api.eth.BlockChain().GetBlockByHash(parentHash) == nil {
+		return nil, engine.UnknownParent
+	}
+
 	args := &miner.BuildInclusionListArgs{
 		Parent: parentHash,
 	}