diff --git a/doc/fix_ave_spatial.html b/doc/fix_ave_spatial.html
index ac8b182126..8848315c53 100644
--- a/doc/fix_ave_spatial.html
+++ b/doc/fix_ave_spatial.html
@@ -13,7 +13,7 @@
 </H3>
 <P><B>Syntax:</B>
 </P>
-<PRE>fix ID group-ID ave/spatial Nevery Nrepeat Nfreq dim origin delta file style args keyword value ... 
+<PRE>fix ID group-ID ave/spatial Nevery Nrepeat Nfreq dim origin delta style arg keyword args ... 
 </PRE>
 <UL><LI>ID, group-ID are documented in <A HREF = "fix.html">fix</A> command 
 
@@ -39,12 +39,12 @@
   <I>compute</I> arg = compute-ID that stores or calculates per-atom quantities
   <I>fix</I> arg = fix-ID that stores or calculates per-atom quantities 
 </PRE>
-<LI>zero or more keyword/value pairs may be appended 
+<LI>zero or more keyword/arg pairs may be appended 
 
 <LI>keyword = <I>norm</I> or <I>units</I> or <I>file</I> or <I>ave</I> 
 
-<PRE>  <I>units</I> value = <I>box</I> or <I>lattice</I> or <I>reduced</I>
-  <I>norm</I> value = <I>all</I> or <I>sample</I>
+<PRE>  <I>units</I> arg = <I>box</I> or <I>lattice</I> or <I>reduced</I>
+  <I>norm</I> arg = <I>all</I> or <I>sample</I>
   <I>file</I> arg = filename
     filename = file to write results to
   <I>ave</I> args = <I>one</I> or <I>running</I> or <I>window M</I>
@@ -261,7 +261,13 @@ nvalues + 1 and J = N % nvalues + 1.
 the <A HREF = "run.html">run</A> 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>When the <I>ave</I> keyword is set to <I>running</I> or <I>window</I> then the number
+of layers must remain the same during the simulation, so that the
+appropriate averaging can be done.  This will be the case if the
+simulation box size doesn't change or if the <I>units</I> keyword is set to
+<I>reduced</I>.
 </P>
 <P><B>Related commands:</B>
 </P>
diff --git a/doc/fix_ave_spatial.txt b/doc/fix_ave_spatial.txt
index 16ff24abad..924c1ffe7e 100644
--- a/doc/fix_ave_spatial.txt
+++ b/doc/fix_ave_spatial.txt
@@ -10,7 +10,7 @@ fix ave/spatial command :h3
 
 [Syntax:]
 
-fix ID group-ID ave/spatial Nevery Nrepeat Nfreq dim origin delta file style args keyword value ... :pre
+fix ID group-ID ave/spatial Nevery Nrepeat Nfreq dim origin delta style arg keyword args ... :pre
 
 ID, group-ID are documented in "fix"_fix.html command :ulb,l
 ave/spatial = style name of this fix command :l
@@ -26,10 +26,10 @@ style = {density} or {compute} or {fix} :l
     {number} = calculate number density
   {compute} arg = compute-ID that stores or calculates per-atom quantities
   {fix} arg = fix-ID that stores or calculates per-atom quantities :pre
-zero or more keyword/value pairs may be appended :l
+zero or more keyword/arg pairs may be appended :l
 keyword = {norm} or {units} or {file} or {ave} :l
-  {units} value = {box} or {lattice} or {reduced}
-  {norm} value = {all} or {sample}
+  {units} arg = {box} or {lattice} or {reduced}
+  {norm} arg = {all} or {sample}
   {file} arg = filename
     filename = file to write results to
   {ave} args = {one} or {running} or {window M}
@@ -245,7 +245,13 @@ No parameter of this fix 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:]
+
+When the {ave} keyword is set to {running} or {window} then the number
+of layers must remain the same during the simulation, so that the
+appropriate averaging can be done.  This will be the case if the
+simulation box size doesn't change or if the {units} keyword is set to
+{reduced}.
 
 [Related commands:]