diff --git a/notebooks/chap12.ipynb b/notebooks/chap12.ipynb
index eb41ffe0..50a9c232 100644
--- a/notebooks/chap12.ipynb
+++ b/notebooks/chap12.ipynb
@@ -746,7 +746,7 @@
     "    add_immunization(system, fraction)\n",
     "    add_hand_washing(system, spending)\n",
     "    \n",
-    "    results, run_simulation(system, update_func)\n",
+    "    results = run_simulation(system, update_func)\n",
     "    print(doses, system.init.S, system.beta, calc_total_infected(results))"
    ]
   },