diff --git a/examples/p4est_2d_dgsem/elixir_euler_airfoil_mach2.jl b/examples/p4est_2d_dgsem/elixir_euler_airfoil_mach2.jl
index 55efabcd346..55005704d1a 100644
--- a/examples/p4est_2d_dgsem/elixir_euler_airfoil_mach2.jl
+++ b/examples/p4est_2d_dgsem/elixir_euler_airfoil_mach2.jl
@@ -73,10 +73,10 @@ boundary_symbols = [:PhysicalLine10, :PhysicalLine20, :PhysicalLine30, :Physical
 
 mesh = P4estMesh{2}(mesh_file, polydeg = d, boundary_symbols = boundary_symbols)
 
-boundary_conditions = Dict(:PhysicalLine10 => boundary_condition_supersonic_inflow,
+boundary_conditions = Dict(:PhysicalLine10 => boundary_condition_supersonic_inflow, # Left boundary
                            :PhysicalLine20 => boundary_condition_outflow, # Right boundary
                            :PhysicalLine30 => boundary_condition_slip_wall, # Airfoil
-                           :PhysicalLine40 => boundary_condition_outflow)
+                           :PhysicalLine40 => boundary_condition_outflow) # Top and bottom boundary
 
 semi = SemidiscretizationHyperbolic(mesh, equations, initial_condition, solver,
                                     boundary_conditions = boundary_conditions)