Index: fenics-dolfinx/python/demo/demo_half_loaded_waveguide.py
===================================================================
--- fenics-dolfinx.orig/python/demo/demo_half_loaded_waveguide.py	2025-11-26 12:52:10.543328627 +0100
+++ fenics-dolfinx/python/demo/demo_half_loaded_waveguide.py	2025-11-26 12:52:10.540834884 +0100
@@ -466,7 +466,7 @@
 
         if has_vtx:
             # Save solutions
-            with VTXWriter(msh.comm, out_folder / f"/Et_{i}.bp", Et_dg) as f:
+            with VTXWriter(msh.comm, out_folder / f"Et_{i}.bp", Et_dg) as f:
                 f.write(0.0)
 
             with VTXWriter(msh.comm, out_folder / f"sols/Ez_{i}.bp", ezh) as f: