diff --git a/examples/jupyter/post-processing.ipynb b/examples/jupyter/post-processing.ipynb
index 72fb73758a..b0e9552983 100644
--- a/examples/jupyter/post-processing.ipynb
+++ b/examples/jupyter/post-processing.ipynb
@@ -105,7 +105,7 @@
    "outputs": [],
    "source": [
     "# Instantiate a Materials collection\n",
-    "materials_file = openmc.Materials((fuel, water, zircaloy))\n",
+    "materials_file = openmc.Materials([fuel, water, zircaloy])\n",
     "\n",
     "# Export to \"materials.xml\"\n",
     "materials_file.export_to_xml()"