diff --git a/build.sh b/build.sh
index 9a7ee3b..ac08c4c 100755
--- a/build.sh
+++ b/build.sh
@@ -15,7 +15,7 @@ pdfjam cover.pdf '1,{},{},2' --outfile cover.pdf
 pages=$(pdfinfo guts.pdf | awk '/^Pages:/ {print $2}')
 let rem=pages%4
 let extra=(4-rem)%4
-let sig=pages+rem
+let sig=pages+extra
 
 # booklet print
 pdfbook2 -n --short-edge cover.pdf
diff --git a/doc.md b/doc.md
index 0558a44..d48ed0a 100644
--- a/doc.md
+++ b/doc.md
@@ -97,7 +97,7 @@ pdfjam cover.pdf '1,{},{},2' --outfile cover.pdf
 pages=$(pdfinfo guts.pdf | awk '/^Pages:/ {print $2}')
 let rem=pages%4
 let extra=$((4-rem))%4
-let sig=pages+rem
+let sig=pages+extra
 
 # booklet print
 pdfbook2 -n --short-edge cover.pdf