diff --git a/doc/fix_atc.html b/doc/fix_atc.html
index 8ee90012dc..7e742ece00 100644
--- a/doc/fix_atc.html
+++ b/doc/fix_atc.html
@@ -141,7 +141,12 @@ can be used with the <I>start/stop</I> keywords of the <A HREF = "run.html">run<
 command.  This fix is not invoked during <A HREF = "minimize.html">energy
 minimization</A>.
 </P>
-<P><B>Restrictions:</B> none
+<P><B>Restrictions:</B>
+</P>
+<P>This fix is part of the "user-atc" package.  It is only enabled if
+LAMMPS was built with that package, which also requires the ATC
+library be built and linked with LAMMPS.  See the <A HREF = "Section_start.html#2_3">Making
+LAMMPS</A> section for more info.
 </P>
 <P><B>Related commands:</B>
 </P>
diff --git a/doc/fix_atc.txt b/doc/fix_atc.txt
index 90728f26cd..619937d5b2 100644
--- a/doc/fix_atc.txt
+++ b/doc/fix_atc.txt
@@ -135,7 +135,12 @@ can be used with the {start/stop} keywords of the "run"_run.html
 command.  This fix is not invoked during "energy
 minimization"_minimize.html.
 
-[Restrictions:] none
+[Restrictions:]
+
+This fix is part of the "user-atc" package.  It is only enabled if
+LAMMPS was built with that package, which also requires the ATC
+library be built and linked with LAMMPS.  See the "Making
+LAMMPS"_Section_start.html#2_3 section for more info.
 
 [Related commands:]