diff --git a/src/app/modules/submission/__tests__/submission.service.spec.ts b/src/app/modules/submission/__tests__/submission.service.spec.ts
index d97de25f05..6436e1a4dc 100644
--- a/src/app/modules/submission/__tests__/submission.service.spec.ts
+++ b/src/app/modules/submission/__tests__/submission.service.spec.ts
@@ -1914,6 +1914,30 @@ describe('submission.service', () => {
       expect(result._unsafeUnwrapErr()).toEqual(new InvalidFileExtensionError())
     })
 
+    it('should reject submissions when attachment responses are invalid', async () => {
+      // Special case where we found instances where the filename was not a string
+      // See https://www.notion.so/opengov/TypeError-Cannot-read-properties-of-undefined-reading-split-in-file-validation-js-6f4dcc17e6fc48319d8f7f0f997685c2?pvs=4
+      // We can remove this test case when the issue is found and fixed
+      const processedResponse1 = generateNewAttachmentResponse({
+        content: readFileSync('./__tests__/unit/backend/resources/invalid.py'),
+        filename: 'mock.jpg',
+      })
+
+      processedResponse1.filename = null as unknown as string
+
+      // Omit attributes only present in processed fields
+      const response1 = omit(processedResponse1, [
+        'isVisible',
+        'isUserVerified',
+      ])
+
+      const result = await SubmissionService.validateAttachments(
+        [response1],
+        FormResponseMode.Email,
+      )
+      expect(result._unsafeUnwrapErr()).toEqual(new InvalidFileExtensionError())
+    })
+
     it('should reject submissions when there are invalid file types in zip', async () => {
       const processedResponse1 = generateNewAttachmentResponse({
         content: readFileSync(
diff --git a/src/app/modules/submission/__tests__/submission.utils.spec.ts b/src/app/modules/submission/__tests__/submission.utils.spec.ts
index 87f3876943..a594bfa240 100644
--- a/src/app/modules/submission/__tests__/submission.utils.spec.ts
+++ b/src/app/modules/submission/__tests__/submission.utils.spec.ts
@@ -111,6 +111,16 @@ describe('submission.utils', () => {
   })
 
   describe('getInvalidFileExtensions', () => {
+    it('should throw error when filename is not a string', async () => {
+      // Special case where we found instances where the filename was not a string
+      // See https://www.notion.so/opengov/TypeError-Cannot-read-properties-of-undefined-reading-split-in-file-validation-js-6f4dcc17e6fc48319d8f7f0f997685c2?pvs=4
+      // We can remove this test case when the issue is found and fixed
+      const promiseOutcome = getInvalidFileExtensions([
+        { ...validSingleFile, filename: null as unknown as string },
+      ])
+      await expect(promiseOutcome).toReject()
+    })
+
     it('should return empty array when given a single valid file', async () => {
       const invalid = await getInvalidFileExtensions([validSingleFile])
       expect(invalid).toEqual([])
diff --git a/src/app/modules/submission/submission.utils.ts b/src/app/modules/submission/submission.utils.ts
index dcf7f104f8..1cb5fc5698 100644
--- a/src/app/modules/submission/submission.utils.ts
+++ b/src/app/modules/submission/submission.utils.ts
@@ -576,7 +576,21 @@ export const getInvalidFileExtensions = (
   // Turn it into an array of promises that each resolve
   // to an array of file extensions that are invalid (if any)
   const promises = attachments.map((attachment) => {
-    const extension = FileValidation.getFileExtension(attachment.filename)
+    const { filename } = attachment
+    // Special case where we found instances where the filename was not a string
+    // See https://www.notion.so/opengov/TypeError-Cannot-read-properties-of-undefined-reading-split-in-file-validation-js-6f4dcc17e6fc48319d8f7f0f997685c2?pvs=4
+    // We can remove this handling when the issue is found and fixed
+    if (filename == null) {
+      logger.error({
+        message: 'A string is expected, but received null or undefined',
+        meta: {
+          action: 'getInvalidFileExtensions',
+          filename,
+        },
+      })
+      return Promise.reject(new Error('filename is required'))
+    }
+    const extension = FileValidation.getFileExtension(filename)
     if (FileValidation.isInvalidFileExtension(extension)) {
       return Promise.resolve([extension])
     }