diff --git a/book/content/modelling/03_compartments/01_fundamentals.ipynb b/book/content/modelling/03_compartments/01_fundamentals.ipynb
index 6550336b..97a0c7c5 100644
--- a/book/content/modelling/03_compartments/01_fundamentals.ipynb
+++ b/book/content/modelling/03_compartments/01_fundamentals.ipynb
@@ -33,7 +33,7 @@
     "\n",
     "<img src=\"./figs/compartment_fire_setup_01.png\" width=\"60%\">\n",
     "\n",
-    "Setup for the compartment fire example. There is only a single opening, i.e. the door. The surface with a predefined heat release rate is indicated in red.\n",
+    "Setup for the compartment fire example. There is only one single opening, i.e. the door. The surface with a predefined heat release rate is indicated in red.\n",
     ":::\n",
     "\n",
     "The heat release rate is defined as a constant value of $\\mf 10~kW$ and the patch emitting the fuel has a surface temperature of $\\mf 100~^\\circ C$.\n",