diff --git a/doc/src/fix_deform_pressure.rst b/doc/src/fix_deform_pressure.rst
index 1490390988..25ad5bfeca 100644
--- a/doc/src/fix_deform_pressure.rst
+++ b/doc/src/fix_deform_pressure.rst
@@ -311,6 +311,10 @@ This fix is not invoked during :doc:`energy minimization <minimize>`.
 Restrictions
 """"""""""""
 
+This fix is part of the EXTRA-FIX package.  It is only enabled if LAMMPS
+was built with that package.  See the :doc:`Build package <Build_package>`
+page for more info.
+
 You cannot apply x, y, or z deformations to a dimension that is
 shrink-wrapped via the :doc:`boundary <boundary>` command.