diff --git a/packages/backend-core/src/cache/docWritethrough.ts b/packages/backend-core/src/cache/docWritethrough.ts
index 9e1977f797..13a85a0d84 100644
--- a/packages/backend-core/src/cache/docWritethrough.ts
+++ b/packages/backend-core/src/cache/docWritethrough.ts
@@ -19,9 +19,9 @@ interface CacheItem {
 }
 
 export class DocWritethrough {
-  db: Database
-  docId: string
-  writeRateMs: number
+  private db: Database
+  private _docId: string
+  private writeRateMs: number
 
   constructor(
     db: Database,
@@ -29,10 +29,14 @@ export class DocWritethrough {
     writeRateMs: number = DEFAULT_WRITE_RATE_MS
   ) {
     this.db = db
-    this.docId = docId
+    this._docId = docId
     this.writeRateMs = writeRateMs
   }
 
+  get docId() {
+    return this._docId
+  }
+
   private makeCacheItem(): CacheItem {
     return { lastWrite: Date.now() }
   }
diff --git a/packages/backend-core/src/cache/tests/docWritethrough.spec.ts b/packages/backend-core/src/cache/tests/docWritethrough.spec.ts
index 16e47ce3c3..aed87499ee 100644
--- a/packages/backend-core/src/cache/tests/docWritethrough.spec.ts
+++ b/packages/backend-core/src/cache/tests/docWritethrough.spec.ts
@@ -41,8 +41,9 @@ describe("docWritethrough", () => {
       docWritethrough = new DocWritethrough(db, documentId, WRITE_RATE_MS)
     })
 
-    it("patching will not persist if timeout does not hit", async () => {
+    it("patching will not persist if timeout from the creation does not hit", async () => {
       await config.doInTenant(async () => {
+        travelForward(WRITE_RATE_MS)
         await docWritethrough.patch(generatePatchObject(2))
         await docWritethrough.patch(generatePatchObject(2))
         travelForward(WRITE_RATE_MS - 1)
@@ -116,7 +117,7 @@ describe("docWritethrough", () => {
       await config.doInTenant(async () => {
         const patch1 = generatePatchObject(2)
         await docWritethrough.patch(patch1)
-        const time1 = travelForward(WRITE_RATE_MS)
+        travelForward(WRITE_RATE_MS)
         const patch2 = generatePatchObject(1)
         await docWritethrough.patch(patch2)
 
@@ -144,5 +145,41 @@ describe("docWritethrough", () => {
         )
       })
     })
+
+    it("concurrent patches to multiple DocWritethrough will not contaminate each other", async () => {
+      await config.doInTenant(async () => {
+        const secondDocWritethrough = new DocWritethrough(
+          db,
+          structures.db.id(),
+          WRITE_RATE_MS
+        )
+
+        const doc1Patch = generatePatchObject(2)
+        await docWritethrough.patch(doc1Patch)
+        const doc2Patch = generatePatchObject(1)
+        await secondDocWritethrough.patch(doc2Patch)
+
+        travelForward(WRITE_RATE_MS)
+
+        const doc1Patch2 = generatePatchObject(3)
+        await docWritethrough.patch(doc1Patch2)
+        const doc2Patch2 = generatePatchObject(3)
+        await secondDocWritethrough.patch(doc2Patch2)
+
+        expect(await db.get(docWritethrough.docId)).toEqual(
+          expect.objectContaining({
+            ...doc1Patch,
+            ...doc1Patch2,
+          })
+        )
+
+        expect(await db.get(secondDocWritethrough.docId)).toEqual(
+          expect.objectContaining({
+            ...doc2Patch,
+            ...doc2Patch2,
+          })
+        )
+      })
+    })
   })
 })