diff --git a/web3/engine_api_callsigs.nim b/web3/engine_api_callsigs.nim
index d4ada4c..471af07 100644
--- a/web3/engine_api_callsigs.nim
+++ b/web3/engine_api_callsigs.nim
@@ -4,4 +4,4 @@ import ethtypes, engine_api_types
 
 proc engine_executePayloadV1(payload: ExecutionPayloadV1): ExecutePayloadResponse
 proc engine_forkchoiceUpdatedV1(forkchoiceState: ForkchoiceStateV1, payloadAttributes: Option[PayloadAttributesV1]): ForkchoiceUpdatedResponse
-proc engine_getPayloadV1(payloadId: Quantity): ExecutionPayloadV1
+proc engine_getPayloadV1(payloadId: PayloadID): ExecutionPayloadV1
diff --git a/web3/engine_api_types.nim b/web3/engine_api_types.nim
index 8b824d2..164965b 100644
--- a/web3/engine_api_types.nim
+++ b/web3/engine_api_types.nim
@@ -19,6 +19,8 @@ type
     invalid = "INVALID"
     syncing = "SYNCING"
 
+  PayloadID* = FixedBytes[8]
+
   ExecutePayloadResponse* = object
     status*: string
     latestValidHash*: Option[BlockHash]
@@ -36,7 +38,7 @@ type
 
   ForkchoiceUpdatedResponse* = object
     status*: string
-    payloadId*: Option[Quantity]
+    payloadId*: Option[PayloadID]
 
 const
   # https://github.com/ethereum/execution-apis/blob/v1.0.0-alpha.4/src/engine/interop/specification.md#error-codes