diff --git a/README.pod b/README.pod
index ce3ea97..6f2f4ea 100644
--- a/README.pod
+++ b/README.pod
@@ -586,8 +586,8 @@ C<--xticlabels>
 If given, the x-axis tic labels are not numerical, but are read from the data.
 This changes the interpretation of the input data: with C<--domain>, each line
 begins with C<x label ....>. Without C<--domain>, each line begins with C<label
-...>. This does I<not> affect the tuple size. This makes sense only without
-C<--3d>. Please see the guide
+...>. Clearly, the labels may not contain whitespace. This does I<not> affect
+the tuple size. This makes sense only without C<--3d>. Please see the guide
 (L<https://github.com/dkogan/feedgnuplot/blob/master/guide/guide.org>) for usage
 examples.
 
diff --git a/bin/feedgnuplot b/bin/feedgnuplot
index 9af8bd9..981d89e 100755
--- a/bin/feedgnuplot
+++ b/bin/feedgnuplot
@@ -1995,8 +1995,8 @@ C<--xticlabels>
 If given, the x-axis tic labels are not numerical, but are read from the data.
 This changes the interpretation of the input data: with C<--domain>, each line
 begins with C<x label ....>. Without C<--domain>, each line begins with C<label
-...>. This does I<not> affect the tuple size. This makes sense only without
-C<--3d>. Please see the guide
+...>. Clearly, the labels may not contain whitespace. This does I<not> affect
+the tuple size. This makes sense only without C<--3d>. Please see the guide
 (L<https://github.com/dkogan/feedgnuplot/blob/master/guide/guide.org>) for usage
 examples.
 
diff --git a/guide/guide.org b/guide/guide.org
index 0d6b2e8..416b23d 100644
--- a/guide/guide.org
+++ b/guide/guide.org
@@ -538,8 +538,8 @@ These aren't "histograms", where gnuplot bins the data for us, but rather the
 data is given to us, ready to plot. We pass =--xticlabels= to indicate that the
 x-axis tic labels come from the data. This changes the interpretation of the
 input: with =--domain=, each line begins with =x label ....=. Without
-=--domain=, each line begins with =label ...=. This does /not/ affect the
-tuple size.
+=--domain=, each line begins with =label ...=. Clearly, the labels may not
+contain whitespace. This does /not/ affect the tuple size.
 
 Basic example without =--domain=: