diff --git a/NonLinearSolver/contact/contactTerms.cpp b/NonLinearSolver/contact/contactTerms.cpp
index 24af17d5b8da4e4545d4b41dd945b54da58946fc..0a9f532e75f059b98d9ba47ff7062cea1518fc7c 100644
--- a/NonLinearSolver/contact/contactTerms.cpp
+++ b/NonLinearSolver/contact/contactTerms.cpp
@@ -84,7 +84,7 @@ template<> void defoDefoContactBilinearTermByPerturbation<double>::get(contactEl
     disp(j)+=_pert;
     for(int i=0; i<nbdofs; i++)
     {
-      m(i,j)=(Fplus(i)-Fminus(i))/(-2.*_pert); //minus because stiffness related toof internal force
+      m(i,j)=(Fplus(i)-Fminus(i))/(2.*_pert); //
     }
   }
   defoDefoTerm->get(cE,npts,GP,Fminus,disp);// put back the right _nodesInContact