diff --git a/src/tree.py b/src/tree.py
index 1a43375c226a1bca494459af9c4e174ea43862e3..692eff50aef8ea6a8dc683401930b5369f5ffef3 100644
--- a/src/tree.py
+++ b/src/tree.py
@@ -303,6 +303,9 @@ class TreeWalker:
         for e in config.get("export", []):
             full_name = os.path.join(section_path, e)
             exercise = load_json(full_name)
-            if "exercise_id" not in exercise:
-                exercise["exercise_id"] = uuid.uuid4().hex
+            if "exercise_id" not in exercise or exercise.get("exercise_id") in id_set:
+                eid = uuid.uuid4().hex
+                exercise["exercise_id"] = eid
                 dump_json(full_name, exercise, True, True)
+            else:
+                id_set.add(exercise["exercise_id"])