diff --git a/user-doc/tutorials/aa-lugano-6b.txt b/user-doc/tutorials/aa-lugano-6b.txt
index fb56db608e5ecff929b8df08c446fa61031f7262..5543d01378aca9d8cea65ab0117b4b0d5d3772f7 100644
--- a/user-doc/tutorials/aa-lugano-6b.txt
+++ b/user-doc/tutorials/aa-lugano-6b.txt
@@ -115,7 +115,7 @@ In order to do so, normalize it adding the correct entropic term \f$ k_BT \log d
 a region where the free energy is approximately constant to represent the bulk region.
 You can for instance use the following commands in gnuplot
 \verbatim
-gnuplot> p "fes_dc" u 1:2 , "" u 1:($2+2.5*log($1)
+gnuplot> p "fes_dc" u 1:2 , "" u 1:($2+2.5*log($1**2))
 \endverbatim
 
 Below you can find reference results