diff --git a/web/src/upload.ts b/web/src/upload.ts
index 11dd402b1f..cbc9802046 100644
--- a/web/src/upload.ts
+++ b/web/src/upload.ts
@@ -534,7 +534,7 @@ export function initialize(): void {
         if (compose_state.composing()) {
             // Compose box is open; drop there.
             upload_files(compose_upload_object, compose_config, files);
-        } else if ($last_drag_drop_edit_container.length !== 0) {
+        } else if ($last_drag_drop_edit_container[0] !== undefined) {
             // A message edit box is open; drop there.
             const row_id = rows.get_message_id($last_drag_drop_edit_container[0]);
             const $drag_drop_container = edit_config(row_id).drag_drop_container();
diff --git a/web/tests/upload.test.js b/web/tests/upload.test.js
index 5bab39ee5e..cd15479fd1 100644
--- a/web/tests/upload.test.js
+++ b/web/tests/upload.test.js
@@ -754,7 +754,7 @@ test("main_file_drop_edit_mode", ({override, override_rewire}) => {
         dropped_row_id = config.row;
         upload_files_called = true;
     });
-    $(".message_edit_form form").last = () => ({length: 1});
+    $(".message_edit_form form").last = () => ({length: 1, [0]: "stub"});
     override(rows, "get_message_id", () => 40);
 
     // Edit box which registered the event handler no longer exists.
@@ -776,7 +776,7 @@ test("main_file_drop_edit_mode", ({override, override_rewire}) => {
 
     override(rows, "get_message_id", () => 40);
     // Edit box open
-    $(".message_edit_form form").last = () => ({length: 1});
+    $(".message_edit_form form").last = () => ({length: 1, [0]: "stub"});
     drop_handler(drop_event);
     assert.equal(upload_files_called, true);
     assert.equal(dropped_row_id, 40);