diff --git a/cbz2ebook.sh b/cbz2ebook.sh
index b083e77..931b1d7 100755
--- a/cbz2ebook.sh
+++ b/cbz2ebook.sh
@@ -1,8 +1,10 @@
 #!/bin/zsh -i
 set -e
 
-SIZE="1440x1920" # Kobo Forma
-#SIZE="768x1024" # Amazon Kindle Paperwhite
+size="1440x1920" # Kobo Forma
+#size="768x1024" # Amazon Kindle Paperwhite
+
+vertical_size="$(cut -dx -f2 <<< $size)x$(cut -dx -f1 <<< $size)"
 
 infile="$(realpath $1)"
 outfile="$(realpath $2)"
@@ -23,9 +25,9 @@ for image in **/*; do
     width=$(identify -format "%W" "$image")
     height=$(identify -format "%H" "$image")
     if (($width > $height)); then
-        mogrify -resize "$SIZE" -rotate 270 "$image"
+        mogrify -resize "$vertical_size" -rotate 270 "$image"
     else
-        mogrify -resize "$SIZE" "$image"
+        mogrify -resize "$size" "$image"
     fi
     position=$(($position + 1))
     echo -ne "$(printf '%3s' $((100 * $position / $length))) %   "$(printf "%0*d" "$((72 * $position / $length))" 0 | tr '0' '#')'\r'