diff --git a/storage-test.sh b/storage-test.sh
index 48af1cf..c8f0955 100755
--- a/storage-test.sh
+++ b/storage-test.sh
@@ -108,7 +108,7 @@ if [ "$1" = "" ]; then
   df=0
   drives="$(df | grep ext4)"
   echo "$drives" | while IFS= read -r line ; do
-	  (($df++))
+	  ((df++))
 	  echo "$df) $line"
   done