diff --git a/build.sh b/build.sh
index 50b88e8..6750e51 100755
--- a/build.sh
+++ b/build.sh
@@ -3,9 +3,9 @@
 set -x -o pipefail
 
 tag=$1
-build=${$2:-0}
+build=$2
 
 docker build -t ${tag}:latest .
-if [[ $build -gt 0 ]]; then
+if [[ $build == "" ]]; then
     docker build -t ${tag}:${build} .
 fi