diff --git a/.changeset/beige-clocks-mix.md b/.changeset/beige-clocks-mix.md
new file mode 100644
index 000000000..1b0099006
--- /dev/null
+++ b/.changeset/beige-clocks-mix.md
@@ -0,0 +1,5 @@
+---
+'@powersync/service-core': patch
+---
+
+Internal: Improve types for oplog data
diff --git a/packages/service-core/src/sync/sync.ts b/packages/service-core/src/sync/sync.ts
index 9ea5fd794..cc8bfea30 100644
--- a/packages/service-core/src/sync/sync.ts
+++ b/packages/service-core/src/sync/sync.ts
@@ -440,7 +440,7 @@ async function* bucketDataBatch(request: BucketDataRequest): AsyncGenerator<Buck
   }
 }
 
-function transformLegacyResponse(bucketData: util.SyncBucketData): any {
+function transformLegacyResponse(bucketData: util.SyncBucketData): util.SyncBucketData<util.ProtocolOplogData> {
   return {
     ...bucketData,
     data: bucketData.data.map((entry) => {
diff --git a/packages/service-core/src/util/protocol-types.ts b/packages/service-core/src/util/protocol-types.ts
index d68738cbf..d061e16d1 100644
--- a/packages/service-core/src/util/protocol-types.ts
+++ b/packages/service-core/src/util/protocol-types.ts
@@ -1,5 +1,6 @@
 import * as t from 'ts-codec';
-import { BucketDescription, BucketPriority, SqliteJsonValue } from '@powersync/service-sync-rules';
+import { BucketDescription, BucketPriority, SqliteJsonRow } from '@powersync/service-sync-rules';
+import { JsonContainer } from '@powersync/service-jsonbig';
 
 export const BucketRequest = t.object({
   name: t.string,
@@ -65,7 +66,7 @@ export interface StreamingSyncCheckpointDiff {
 }
 
 export interface StreamingSyncData {
-  data: SyncBucketData;
+  data: SyncBucketData<ProtocolOplogData>;
 }
 
 export interface StreamingSyncCheckpointComplete {
@@ -109,13 +110,9 @@ export interface BucketState {
   op_id: string;
 }
 
-export interface SyncDataBatch {
-  buckets: SyncBucketData[];
-}
-
-export interface SyncBucketData {
+export interface SyncBucketData<Data extends ProtocolOplogData = StoredOplogData> {
   bucket: string;
-  data: OplogEntry[];
+  data: OplogEntry<Data>[];
   /**
    * True if there _could_ be more data for this bucket, and another request must be made.
    */
@@ -130,12 +127,20 @@ export interface SyncBucketData {
   next_after: ProtocolOpId;
 }
 
-export interface OplogEntry {
+export type StoredOplogData = string | null;
+
+// Note: When clients have both raw_data and binary_data disabled (this only affects legacy
+// clients), data is actually a `Record<string, SqliteJsonValue>`. Oplog entries are always
+// stored as a serialized (JSON) string so that they don't have to be parsed in the sync service,
+// this representation only exists on the way out for legacy clients.
+export type ProtocolOplogData = SqliteJsonRow | JsonContainer | StoredOplogData;
+
+export interface OplogEntry<Data extends ProtocolOplogData = StoredOplogData> {
   op_id: ProtocolOpId;
   op: 'PUT' | 'REMOVE' | 'MOVE' | 'CLEAR';
   object_type?: string;
   object_id?: string;
-  data?: Record<string, SqliteJsonValue> | string | null;
+  data?: Data;
   checksum: number | bigint;
   subkey?: string;
 }
diff --git a/test-client/src/util.ts b/test-client/src/util.ts
index 5c57e1750..51dc4bb3d 100644
--- a/test-client/src/util.ts
+++ b/test-client/src/util.ts
@@ -1,6 +1,8 @@
 import type * as types from '@powersync/service-core';
 
-export type BucketData = Record<string, types.OplogEntry[]>;
+export type TestOplogEntry = types.OplogEntry<types.ProtocolOplogData>;
+
+export type BucketData = Record<string, TestOplogEntry[]>;
 
 /**
  * Combine all chunks of received data, excluding any data after the checkpoint.
@@ -57,8 +59,8 @@ export function isCheckpoint(line: types.StreamingSyncLine): line is types.Strea
  *
  * This is the function $r(B)$, as described in /docs/bucket-properties.md.
  */
-export function reduceBucket(operations: types.OplogEntry[]) {
-  let rowState = new Map<string, types.OplogEntry>();
+export function reduceBucket(operations: TestOplogEntry[]) {
+  let rowState = new Map<string, TestOplogEntry>();
   let otherChecksum = 0;
 
   for (let op of operations) {
@@ -90,7 +92,7 @@ export function reduceBucket(operations: types.OplogEntry[]) {
     return Number(BigInt(a.op_id) - BigInt(b.op_id));
   });
 
-  let finalState: types.OplogEntry[] = [
+  let finalState: TestOplogEntry[] = [
     // Special operation to indiciate the checksum remainder
     { op_id: '0', op: 'CLEAR', checksum: otherChecksum },
     ...puts
@@ -99,7 +101,7 @@ export function reduceBucket(operations: types.OplogEntry[]) {
   return finalState;
 }
 
-function rowKey(entry: types.OplogEntry) {
+function rowKey(entry: TestOplogEntry) {
   return `${entry.object_type}/${entry.object_id}/${entry.subkey}`;
 }