diff --git a/matlab/TCV/tcv_requests_mapping.m b/matlab/TCV/tcv_requests_mapping.m
index cd6b96abf97a61e78548dd8e2536d1e91b01a883..ad1bc170dab3bea172e5cffe6628196f901c8e63 100644
--- a/matlab/TCV/tcv_requests_mapping.m
+++ b/matlab/TCV/tcv_requests_mapping.m
@@ -141,8 +141,8 @@ switch lower(data_request)
   mapping.label = 'gap hfs/lfs';
   mapping.method = 'expression';
   mapping.expression = ['params_eff = gdat_data.gdat_params;params_eff.data_request=''tcv_eq("r_contour","LIUQE.M")'';' ...
-                   'gdat_tmp=gdat_tcv([],params_eff);aa_data(1,:)=min(gdat_tmp.data,[],1)-0.624;' ...
-                    'aa_data(2,:)=1.136-max(gdat_tmp.data,[],1);gdat_tmp.data=aa_data;gdat_tmp.x=[1:2];gdat_tmp.dim{1}=gdat_tmp.x;' ...
+                   'gdat_tmp=gdat_tcv([],params_eff);aa_data(1,:)=min(gdat_tmp.data,[],1)-0.624;aa_data(1,[aa_data(1,:)<0]) = 0.;' ...
+                    'aa_data(2,:)=1.1376-max(gdat_tmp.data,[],1);aa_data(2,[aa_data(2,:)<0]) = 0.;gdat_tmp.data=aa_data;gdat_tmp.x=[1:2];gdat_tmp.dim{1}=gdat_tmp.x;' ...
                    'gdat_tmp.dimunits{1}={''HFS'',''LFS''};gdat_tmp.units=''m'';'];
  case {'gas', 'gas_flux', 'gas_request', 'gas_feedforward','gas_valve'}
   mapping.timedim = 1;