diff --git a/dracut-module-setup.sh b/dracut-module-setup.sh
index ef731fc..fc90912 100755
--- a/dracut-module-setup.sh
+++ b/dracut-module-setup.sh
@@ -196,7 +196,7 @@ cal_netmask_by_prefix() {
     _res="$_first_part"
 
     _tmp=$((_octets_total*_bits_per_octet-_prefix))
-    _zero_bits=$(expr $_tmp % $_bits_per_group)
+    _zero_bits=$((_tmp % _bits_per_group))
     if [[ "$_zero_bits" -ne 0 ]]; then
         _second_part=$((_max_group_value >> _zero_bits << _zero_bits))
         if ((_ipv6)); then
diff --git a/kdumpctl b/kdumpctl
index 2226417..3e92804 100755
--- a/kdumpctl
+++ b/kdumpctl
@@ -772,7 +772,7 @@ check_and_wait_network_ready()
 		fi
 
 		cur=$(date +%s)
-		let "diff = $cur - $start_time"
+		diff=$((cur - start_time))
 		# 60s time out
 		if [ $diff -gt 180 ]; then
 			break;
@@ -835,7 +835,7 @@ show_reserved_mem()
     local mem_mb
 
     mem=$(</sys/kernel/kexec_crash_size)
-    mem_mb=$(expr "$mem" / 1024 / 1024)
+    mem_mb=$((mem / 1024 / 1024))
 
     dinfo "Reserved "$mem_mb"MB memory for crash kernel"
 }