diff --git a/src/define_isostasy_bc.f90 b/src/define_isostasy_bc.f90
index df17ee1876f97d2782d10224e5d5c8fbd7fc10fe..7da83b66cdf969f1029fe279498c52bdfe0f8059 100644
--- a/src/define_isostasy_bc.f90
+++ b/src/define_isostasy_bc.f90
@@ -52,7 +52,7 @@ logical firstcall
 !------------------------------------------------------------------------------|
 
 integer i,j,iproc,nproc,ierr,nb,xdisp,ydisp,xnow,ynow,ie,jp
-double precision eps,pi,zsl,dxy,zdisp,vinit
+double precision eps,pi,zsl,dxy,zdisp,vinit,x1,x2
 double precision,dimension(:,:),allocatable::zisoslx,zisosly
 
 !------------------------------------------------------------------------------|