diff --git a/stacks_queues/sort_stack/sort_stack_challenge.ipynb b/stacks_queues/sort_stack/sort_stack_challenge.ipynb
index 3dd087b..3197dd8 100644
--- a/stacks_queues/sort_stack/sort_stack_challenge.ipynb
+++ b/stacks_queues/sort_stack/sort_stack_challenge.ipynb
@@ -153,7 +153,12 @@
     "def main():\n",
     "    test = TestSortStack()\n",
     "    test.test_sort_stack(MyStack())\n",
-    "    test.test_sort_stack(MyStackSimplified())\n",
+    "    try:\n",
+    "        test.test_sort_stack(MyStackSimplified())\n",
+    "    except NameError:\n",
+    "        # Alternate solutions are only defined\n",
+    "        # in the solutions file\n",
+    "        pass\n",
     "\n",
     "\n",
     "if __name__ == '__main__':\n",