diff --git a/bin/build.sh b/bin/build.sh
index 89fe2944..f345ebd2 100755
--- a/bin/build.sh
+++ b/bin/build.sh
@@ -22,7 +22,7 @@ RUN_DOCKERFILE_DIR="heroku-${STACK_VERSION}"
 BUILD_IMAGE_TAG="heroku/heroku:${STACK_VERSION}-build"
 BUILD_DOCKERFILE_DIR="${RUN_DOCKERFILE_DIR}-build"
 
-if [ $STACK_VERSION -ge 24 ]; then
+if [ "$STACK_VERSION" -ge 24 ]; then
     # heroku/heroku:24 images and beyond are multiarch images. Additionally,
     # the CNB specific modifications are included (separate *cnb* variants
     # do not exist).