diff --git a/tasks/task_07_CSG_cell_tally_spectra/2_example_neutron_spectra_on_cell.ipynb b/tasks/task_07_CSG_cell_tally_spectra/2_example_neutron_spectra_on_cell.ipynb
index a296ba12..92268920 100644
--- a/tasks/task_07_CSG_cell_tally_spectra/2_example_neutron_spectra_on_cell.ipynb
+++ b/tasks/task_07_CSG_cell_tally_spectra/2_example_neutron_spectra_on_cell.ipynb
@@ -42,8 +42,8 @@
     "\n",
     "# Due to the hydrogen content water is a very good neutron moderator\n",
     "my_material = openmc.Material()\n",
-    "my_material.add_element('H', 1, percent_type='ao')\n",
-    "my_material.add_element('O', 2, percent_type='ao')\n",
+    "my_material.add_element('H', 2, percent_type='ao')\n",
+    "my_material.add_element('O', 1, percent_type='ao')\n",
     "my_material.set_density('g/cm3', 1)\n",
     "\n",
     "my_materials = openmc.Materials([my_material])\n",