diff --git a/platforms/common/spack_utils.sh b/platforms/common/spack_utils.sh
index 3b7d56aab5e5719436d000dd12f670e0f8bc9447..3372a90da627971679263089d0e0806eec44b433 100644
--- a/platforms/common/spack_utils.sh
+++ b/platforms/common/spack_utils.sh
@@ -9,10 +9,10 @@ function _install_spack() {
   if [ ! -z "${SPACK_UPSTREAMS}" ]; then
     UPSTREAMS_CONFIG=${SPACK_ROOT}/etc/spack/upstreams.yaml
     echo "upstreams:" > $UPSTREAMS_CONFIG
-    let i=0
+    i=0
     for UP in ${SPACK_UPSTREAMS}; do
       echo "Adding upstream repo to config $UPSTREAMS_CONFIG <= $UP"
-      let i=$((i+1))
+      i=$((i+1))
       cat << EOF >> $UPSTREAMS_CONFIG
   spack-instance-$i:
       install_tree: $UP/spack/opt/spack