diff --git a/build.sh b/build.sh
index b301c88..1565c9a 100755
--- a/build.sh
+++ b/build.sh
@@ -14,4 +14,5 @@ pandoc \
 --output "${OUTPUT}/index.html" \
 --write 'revealjs' \
 -V revealjs-url='/sw/revealjs/up' \
+-V slideNumber='true' \
 "${ROOT}/index.md"