diff --git a/meta-google/recipes-google/nftables/files/nft-configure.sh b/meta-google/recipes-google/nftables/files/nft-configure.sh
index 8c8e058..c3805d9 100644
--- a/meta-google/recipes-google/nftables/files/nft-configure.sh
+++ b/meta-google/recipes-google/nftables/files/nft-configure.sh
@@ -6,7 +6,7 @@
   for file in "$dir"/*.rules; do
     basemap["${file##*/}$i"]="$file"
   done
-  let i+=1
+  (( i+=1 ))
 done
 
 rules=""