diff --git a/services/history-v1/storage/lib/chunk_store/postgres.js b/services/history-v1/storage/lib/chunk_store/postgres.js
index 857281151a..d53c796c0b 100644
--- a/services/history-v1/storage/lib/chunk_store/postgres.js
+++ b/services/history-v1/storage/lib/chunk_store/postgres.js
@@ -14,8 +14,8 @@ const DUPLICATE_KEY_ERROR_CODE = '23505'
  * @param {boolean} [opts.readOnly]
  */
 async function getLatestChunk(projectId, opts = {}) {
+  assert.postgresId(projectId, `bad projectId ${projectId}`)
   projectId = parseInt(projectId, 10)
-  assert.integer(projectId, 'bad projectId')
   const { readOnly = false } = opts
 
   const record = await (readOnly ? knexReadOnly : knex)('chunks')
@@ -32,8 +32,8 @@ async function getLatestChunk(projectId, opts = {}) {
  * Get the metadata for the chunk that contains the given version.
  */
 async function getChunkForVersion(projectId, version) {
+  assert.postgresId(projectId, `bad projectId ${projectId}`)
   projectId = parseInt(projectId, 10)
-  assert.integer(projectId, 'bad projectId')
 
   const record = await knex('chunks')
     .where('doc_id', projectId)
@@ -51,8 +51,8 @@ async function getChunkForVersion(projectId, version) {
  * the given timestamp.
  */
 async function getChunkForTimestamp(projectId, timestamp) {
+  assert.postgresId(projectId, `bad projectId ${projectId}`)
   projectId = parseInt(projectId, 10)
-  assert.integer(projectId, 'bad projectId')
 
   // This query will find the latest chunk after the timestamp (query orders
   // in reverse chronological order), OR the latest chunk
@@ -95,8 +95,8 @@ function chunkFromRecord(record) {
  * Get all of a project's chunk ids
  */
 async function getProjectChunkIds(projectId) {
+  assert.postgresId(projectId, `bad projectId ${projectId}`)
   projectId = parseInt(projectId, 10)
-  assert.integer(projectId, 'bad projectId')
 
   const records = await knex('chunks').select('id').where('doc_id', projectId)
   return records.map(record => record.id)
@@ -106,8 +106,8 @@ async function getProjectChunkIds(projectId) {
  * Insert a pending chunk before sending it to object storage.
  */
 async function insertPendingChunk(projectId, chunk) {
+  assert.postgresId(projectId, `bad projectId ${projectId}`)
   projectId = parseInt(projectId, 10)
-  assert.integer(projectId, 'bad projectId')
 
   const result = await knex.first(
     knex.raw("nextval('chunks_id_seq'::regclass)::integer as chunkid")
@@ -127,8 +127,8 @@ async function insertPendingChunk(projectId, chunk) {
  * Record that a new chunk was created.
  */
 async function confirmCreate(projectId, chunk, chunkId) {
+  assert.postgresId(projectId, `bad projectId ${projectId}`)
   projectId = parseInt(projectId, 10)
-  assert.integer(projectId, 'bad projectId')
 
   await knex.transaction(async tx => {
     await Promise.all([
@@ -142,8 +142,8 @@ async function confirmCreate(projectId, chunk, chunkId) {
  * Record that a chunk was replaced by a new one.
  */
 async function confirmUpdate(projectId, oldChunkId, newChunk, newChunkId) {
+  assert.postgresId(projectId, `bad projectId ${projectId}`)
   projectId = parseInt(projectId, 10)
-  assert.integer(projectId, 'bad projectId')
 
   await knex.transaction(async tx => {
     await _deleteChunks(tx, { doc_id: projectId, id: oldChunkId })
@@ -194,8 +194,8 @@ async function _insertChunk(tx, projectId, chunk, chunkId) {
  * @return {Promise}
  */
 async function deleteChunk(projectId, chunkId) {
+  assert.postgresId(projectId, `bad projectId ${projectId}`)
   projectId = parseInt(projectId, 10)
-  assert.integer(projectId, 'bad projectId')
   assert.integer(chunkId, 'bad chunkId')
 
   await _deleteChunks(knex, { doc_id: projectId, id: chunkId })
@@ -205,8 +205,8 @@ async function deleteChunk(projectId, chunkId) {
  * Delete all of a project's chunks
  */
 async function deleteProjectChunks(projectId) {
+  assert.postgresId(projectId, `bad projectId ${projectId}`)
   projectId = parseInt(projectId, 10)
-  assert.integer(projectId, 'bad projectId')
 
   await knex.transaction(async tx => {
     await _deleteChunks(knex, { doc_id: projectId })
diff --git a/services/history-v1/test/acceptance/js/storage/chunk_store_postgres_backend.test.js b/services/history-v1/test/acceptance/js/storage/chunk_store_postgres_backend.test.js
new file mode 100644
index 0000000000..20a24de3eb
--- /dev/null
+++ b/services/history-v1/test/acceptance/js/storage/chunk_store_postgres_backend.test.js
@@ -0,0 +1,48 @@
+const { expect } = require('chai')
+const { ObjectId } = require('mongodb')
+const { Chunk, Snapshot, History } = require('overleaf-editor-core')
+const cleanup = require('./support/cleanup')
+const backend = require('../../../../storage/lib/chunk_store/postgres')
+
+describe('chunk store Postgres backend', function () {
+  beforeEach(cleanup.everything)
+
+  it('should reject ObjectId strings as project IDs', async function () {
+    const invalidProjectId = new ObjectId().toString()
+
+    await expect(backend.getLatestChunk(invalidProjectId)).to.be.rejectedWith(
+      `bad projectId ${invalidProjectId}`
+    )
+    await expect(
+      backend.getChunkForVersion(invalidProjectId, 1)
+    ).to.be.rejectedWith(`bad projectId ${invalidProjectId}`)
+    await expect(
+      backend.getChunkForTimestamp(invalidProjectId, new Date())
+    ).to.be.rejectedWith(`bad projectId ${invalidProjectId}`)
+    await expect(
+      backend.getProjectChunkIds(invalidProjectId)
+    ).to.be.rejectedWith(`bad projectId ${invalidProjectId}`)
+    await expect(
+      backend.insertPendingChunk(invalidProjectId, makeChunk([], 0))
+    ).to.be.rejectedWith(`bad projectId ${invalidProjectId}`)
+    await expect(
+      backend.confirmCreate(invalidProjectId, makeChunk([], 0), 1)
+    ).to.be.rejectedWith(`bad projectId ${invalidProjectId}`)
+    await expect(
+      backend.confirmUpdate(invalidProjectId, 1, makeChunk([], 0), 2)
+    ).to.be.rejectedWith(`bad projectId ${invalidProjectId}`)
+    await expect(backend.deleteChunk(invalidProjectId, 1)).to.be.rejectedWith(
+      `bad projectId ${invalidProjectId}`
+    )
+    await expect(
+      backend.deleteProjectChunks(invalidProjectId)
+    ).to.be.rejectedWith(`bad projectId ${invalidProjectId}`)
+  })
+})
+
+function makeChunk(changes, versionNumber) {
+  const snapshot = Snapshot.fromRaw({ files: {} })
+  const history = new History(snapshot, [])
+  const chunk = new Chunk(history, versionNumber)
+  return chunk
+}