diff --git a/services/docstore/app/js/schemas.js b/services/docstore/app/js/schemas.js
index e57dfdd660..805193dc39 100644
--- a/services/docstore/app/js/schemas.js
+++ b/services/docstore/app/js/schemas.js
@@ -14,17 +14,22 @@ import { z } from '@overleaf/validation-tools'
 // - history restores send id-less changes and comment ops with a `resolved`
 //   flag (stripped again by RangeManager), and detached comments without an
 //   id, see overleaf-editor-core/lib/doc_updater_compatible_ranges.js
+// - old tracked changes created while the fixedRemoveChange flag existed
+//   (removed in https://github.com/overleaf/internal/pull/23993) still carry
+//   it in their op until accepted/rejected
 
 const insertOp = z.strictObject({
   i: z.string(),
   p: z.number().int().min(0),
   u: z.boolean().optional(),
+  fixedRemoveChange: z.boolean().optional(),
 })
 
 const deleteOp = z.strictObject({
   d: z.string(),
   p: z.number().int().min(0),
   u: z.boolean().optional(),
+  fixedRemoveChange: z.boolean().optional(),
 })
 
 const commentOp = z.strictObject({
diff --git a/services/docstore/test/unit/js/schemas.test.js b/services/docstore/test/unit/js/schemas.test.js
new file mode 100644
index 0000000000..8998a9e514
--- /dev/null
+++ b/services/docstore/test/unit/js/schemas.test.js
@@ -0,0 +1,27 @@
+import { describe, it, expect } from 'vitest'
+import { ranges } from '../../../app/js/schemas.js'
+
+describe('schemas', function () {
+  describe('ranges', function () {
+    it('accepts a legacy fixedRemoveChange flag on an insert op', function () {
+      const result = ranges.safeParse({
+        changes: [{ op: { i: 'foo', p: 0, fixedRemoveChange: true } }],
+      })
+      expect(result.success).to.equal(true)
+    })
+
+    it('accepts a legacy fixedRemoveChange flag on a delete op', function () {
+      const result = ranges.safeParse({
+        changes: [{ op: { d: 'foo', p: 0, fixedRemoveChange: true } }],
+      })
+      expect(result.success).to.equal(true)
+    })
+
+    it('rejects an unrecognized key on an insert op', function () {
+      const result = ranges.safeParse({
+        changes: [{ op: { i: 'foo', p: 0, somethingElse: true } }],
+      })
+      expect(result.success).to.equal(false)
+    })
+  })
+})
diff --git a/services/document-updater/app/js/schemas.js b/services/document-updater/app/js/schemas.js
index bb3dd03299..594c0bce5a 100644
--- a/services/document-updater/app/js/schemas.js
+++ b/services/document-updater/app/js/schemas.js
@@ -11,17 +11,23 @@ const { z, zz } = require('@overleaf/validation-tools')
 // schemas model them explicitly: comments/changes preloaded from web may lack `id`.
 // Tightening these is tracked as part of moving the shared editor payload
 // schemas into overleaf-editor-core.
+//
+// Old tracked changes created while the fixedRemoveChange flag existed
+// (removed in https://github.com/overleaf/internal/pull/23993) still carry
+// it in their op until accepted/rejected.
 
 const insertOp = z.strictObject({
   i: z.string(),
   p: z.number().int().min(0),
   u: z.boolean().optional(),
+  fixedRemoveChange: z.boolean().optional(),
 })
 
 const deleteOp = z.strictObject({
   d: z.string(),
   p: z.number().int().min(0),
   u: z.boolean().optional(),
+  fixedRemoveChange: z.boolean().optional(),
 })
 
 const commentOp = z.strictObject({
diff --git a/services/document-updater/test/unit/js/schemas.test.js b/services/document-updater/test/unit/js/schemas.test.js
new file mode 100644
index 0000000000..f3727f737c
--- /dev/null
+++ b/services/document-updater/test/unit/js/schemas.test.js
@@ -0,0 +1,36 @@
+const { expect } = require('chai')
+const { insertOp, deleteOp } = require('../../../app/js/schemas')
+
+describe('schemas', function () {
+  describe('insertOp', function () {
+    it('accepts a legacy fixedRemoveChange flag', function () {
+      const result = insertOp.safeParse({
+        i: 'foo',
+        p: 0,
+        fixedRemoveChange: true,
+      })
+      expect(result.success).to.equal(true)
+    })
+
+    it('rejects an unrecognized key', function () {
+      const result = insertOp.safeParse({ i: 'foo', p: 0, somethingElse: true })
+      expect(result.success).to.equal(false)
+    })
+  })
+
+  describe('deleteOp', function () {
+    it('accepts a legacy fixedRemoveChange flag', function () {
+      const result = deleteOp.safeParse({
+        d: 'foo',
+        p: 0,
+        fixedRemoveChange: true,
+      })
+      expect(result.success).to.equal(true)
+    })
+
+    it('rejects an unrecognized key', function () {
+      const result = deleteOp.safeParse({ d: 'foo', p: 0, somethingElse: true })
+      expect(result.success).to.equal(false)
+    })
+  })
+})