diff --git a/pylib/anki/collection.py b/pylib/anki/collection.py
index 3f88ed4fa..aa1bf4cfd 100644
--- a/pylib/anki/collection.py
+++ b/pylib/anki/collection.py
@@ -195,6 +195,9 @@ crt=?, mod=?, scm=?, dty=?, usn=?, ls=?""",
     def flush_all_changes(self, mod: Optional[int] = None):
         self.models.flush()
         self.decks.flush()
+        # set mod flag if mtime changed by backend
+        if self.db.scalar("select mod from col") != self.mod:
+            self.db.mod = True
         if self.db.mod:
             self.flush(mod)