diff --git a/scripts/generate_fill.py b/scripts/generate_fill.py
index 2b07191..dd4329a 100755
--- a/scripts/generate_fill.py
+++ b/scripts/generate_fill.py
@@ -134,11 +134,11 @@
         print('set xmax [lindex $fullbox 2]', file=ofile)
         print('set xmin [lindex $fullbox 0]', file=ofile)
         print('set fullwidth [expr {$xmax - $xmin}]', file=ofile)
-        print('set xtiles [expr {int(ceil($fullwidth / $stepwidth))}]', file=ofile)
+        print('set xtiles [expr {int(ceil(($fullwidth + 0.0) / $stepwidth))}]', file=ofile)
         print('set ymax [lindex $fullbox 3]', file=ofile)
         print('set ymin [lindex $fullbox 1]', file=ofile)
         print('set fullheight [expr {$ymax - $ymin}]', file=ofile)
-        print('set ytiles [expr {int(ceil($fullheight / $stepheight))}]', file=ofile)
+        print('set ytiles [expr {int(ceil(($fullheight + 0.0) / $stepheight))}]', file=ofile)
         print('box size $stepwidth $stepheight', file=ofile)
         print('set xbase [lindex $fullbox 0]', file=ofile)
         print('set ybase [lindex $fullbox 1]', file=ofile)