diff --git a/doc/src/fix_box_relax.txt b/doc/src/fix_box_relax.txt
index ecbca75908..4430e95a20 100644
--- a/doc/src/fix_box_relax.txt
+++ b/doc/src/fix_box_relax.txt
@@ -315,9 +315,24 @@ specified by the {press} keyword will be unaffected by the {temp}
 setting.
 
 This fix computes a global scalar which can be accessed by various
-"output commands"_Section_howto.html#howto_15.  The scalar is the
+"output commands"_Section_howto.html#howto_15. The scalar is the
 pressure-volume energy, plus the strain energy, if it exists.
 
+This fix computes a global scalar which can be accessed by various
+"output commands"_Section_howto.html#howto_15. The scalar is given
+by the energy expression shown above. The energy values reported
+at the end of a minimization run under "Minimization stats" include
+this energy, and so differ from what LAMMPS normally reports as
+potential energy. This fix does not support the
+"fix_modify"_fix_modify.html {energy} option,
+because that would result in double-counting of the fix energy in the
+minimization energy. Instead, the fix energy can be explicitly
+added to the potential energy using one of these two variants:
+
+variable emin equal pe+f_1  :pre
+
+variable emin equal pe+f_1/atoms :pre
+
 No parameter of this fix can be used with the {start/stop} keywords of
 the "run"_run.html command.