diff --git a/src/backend/app/submission/submission_crud.py b/src/backend/app/submission/submission_crud.py
index 94be8e9c15..ba615de7e9 100644
--- a/src/backend/app/submission/submission_crud.py
+++ b/src/backend/app/submission/submission_crud.py
@@ -468,8 +468,13 @@ def update_submission_in_s3(
             for form in odk_forms
             if form["lastSubmission"] is not None
         ]
-        last_submission = max(
-            valid_datetimes, key=lambda x: datetime.strptime(x, "%Y-%m-%dT%H:%M:%S.%fZ")
+        last_submission = (
+            max(
+                valid_datetimes,
+                key=lambda x: datetime.strptime(x, "%Y-%m-%dT%H:%M:%S.%fZ"),
+            )
+            if valid_datetimes
+            else None
         )
 
         # Check if the file already exists in s3