diff --git a/src/create_surfaces.f90 b/src/create_surfaces.f90
index fba1afbad815a8a965d0713d5e3c8368d45d6cac..b6344bd1b7302a4d0af095f84183b0ff3570ec99 100644
--- a/src/create_surfaces.f90
+++ b/src/create_surfaces.f90
@@ -630,11 +630,11 @@ select case(surface_type)
            if (x(i).le.x1a) then
              zx=sp01
            elseif (x(i).le.x1b) then
-             zx=sp01-((x(i)-x1a)/(-sp06/m))*sp06)
+             zx=sp01-(((x(i)-x1a)/(-sp06/m))*sp06)
            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
@@ -642,11 +642,11 @@ select case(surface_type)
            if (y(i).le.y1a) then
              z(i)=sp01
            elseif (y(i).le.y1b) then
-             z(i)=min(sp01-((y(i)-y1a)/(-sp06/m))*sp06),zx)
+             z(i)=min(sp01-(((y(i)-y1a)/(-sp06/m))*sp06),zx)
            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