diff --git a/cad-based-geometry.ipynb b/cad-based-geometry.ipynb
index 063304a..0b589ef 100644
--- a/cad-based-geometry.ipynb
+++ b/cad-based-geometry.ipynb
@@ -608,6 +608,7 @@
     "settings.batches = 10\n",
     "settings.particles = 5000\n",
     "settings.run_mode = \"fixed source\"\n",
+    "settings.source_rejection_fraction = 1e-5\n",
     "\n",
     "space = openmc.stats.Box(*geometry.bounding_box)\n",
     "my_source = openmc.IndependentSource(space=space, domains=[water])\n",