diff --git a/src/create_surfaces.f90 b/src/create_surfaces.f90
index b6344bd1b7302a4d0af095f84183b0ff3570ec99..f11bb218b83e2f6d1486374f71d54776faa2d609 100644
--- a/src/create_surfaces.f90
+++ b/src/create_surfaces.f90
@@ -634,7 +634,7 @@ select case(surface_type)
            elseif (x(i).le.x2a) then
              zx=sp01-sp06
            elseif (x(i).le.x2b) then
-             zx=sp01-(1.d0+(((x(i)-x2a)/(-sp06/m))*sp06))
+             zx=sp01-((1.d0+((x(i)-x2a)/(-sp06/m)))*sp06)
              !zx=sp01-((1.d0-((x(i)-x2a)/(sp06/m)))*sp06)
            else
              zx=sp01
@@ -646,7 +646,7 @@ select case(surface_type)
            elseif (y(i).le.y2a) then
              z(i)=min(sp01-sp06,zx)
            elseif (y(i).le.y2b) then
-             z(i)=min(sp01-(1.d0+(((y(i)-y2a)/(-sp06/m))*sp06)),zx)
+             z(i)=min(sp01-((1.d0+((y(i)-y2a)/(-sp06/m)))*sp06),zx)
            else
              z(i)=sp01
            endif