diff --git a/doc/src/fix_viscosity.rst b/doc/src/fix_viscosity.rst
index e92d1eab92..204e435d6e 100644
--- a/doc/src/fix_viscosity.rst
+++ b/doc/src/fix_viscosity.rst
@@ -110,10 +110,9 @@ An alternative method for calculating a viscosity is to run a NEMD
 simulation, as described on the :doc:`Howto nemd <Howto_nemd>` doc page.
 NEMD simulations deform the simulation box via the :doc:`fix deform <fix_deform>` command.
 
-Thus they cannot be run on a charged
-system using a :doc:`PPPM solver <kspace_style>` since PPPM does not
-currently support non-orthogonal boxes.  Using fix viscosity keeps the
-box orthogonal; thus it does not suffer from this limitation.
+Some features or combination of settings in LAMMPS do not support
+non-orthogonal boxes.  Using fix viscosity keeps the box orthogonal;
+thus it does not suffer from these limitations.
 
 Restart, fix_modify, output, run start/stop, minimize info
 """""""""""""""""""""""""""""""""""""""""""""""""""""""""""