diff --git a/genplotting.f90 b/genplotting.f90
index 930e18b..110df1a 100644
--- a/genplotting.f90
+++ b/genplotting.f90
@@ -128,6 +128,11 @@ subroutine genp_do_render(srcfile, tgafile, xsize, ysize)
   character (len=20)              :: dima, dimb
   integer                         :: i, j, errcode
 
+  if  (6 .EQ. outunit) then
+    write(0, '(" Sorry, I can not do that, Dave !")')
+    stop " >>> FATAL ERROR"
+  endif
+
   write(0, '("--- genp do_render ---")')
   write(0, '("    srcfile: ", A)') srcfile
   write(0, '("    tgafile: ", A)') tgafile