diff --git a/tools/scroll.sh b/tools/scroll.sh
index 187b1d83..bde5b219 100755
--- a/tools/scroll.sh
+++ b/tools/scroll.sh
@@ -4,5 +4,5 @@ I=0
 while [ 1 ]; do
     sleep 1
     echo $I
-    I=`expr $I + 1`
+    I=$(($I + 1))
 done