diff --git a/run.sh b/run.sh
index c03ee12..f9e2545 100755
--- a/run.sh
+++ b/run.sh
@@ -63,7 +63,7 @@ if [ "${1}" == "update" ]; then
 else
 	[ "${1}" == "clear" ] && rm -f ${MMFOLDER}/mm.*
 	if [ -f ${MMFOLDER}/mm.checking ]; then
-		fd=$(( `date +%s` - `stat -L --format %Y ${MMFOLDER}/mm.checking` ))
+		fd=$(expr $(date +%s) - $(stat -L --format %Y ${MMFOLDER}/mm.checking))
 		if [ ${fd} -gt 900 ]; then
 			rm -f ${MMFOLDER}/mm.checking
 		else