diff --git a/update/nav_rand_logo.sh b/update/nav_rand_logo.sh
index cc5035c..92e598f 100644
--- a/update/nav_rand_logo.sh
+++ b/update/nav_rand_logo.sh
@@ -2,6 +2,9 @@
 
 # 设置图片数量和输出文件名
 IMAGE_NUM_ALL=`ls /opt/websites/nav/assets/images/logos | wc -l`
+# there are 221 logos in total, and index are from 0, so the max index is 220
+# whhereas there has an avatar.jpg file in this dir, so need to subtract one
+let IMAGE_NUM_ALL=IMAGE_NUM_ALL-1
 IMAGE_NUM_NEEDED=`cat /opt/websites/nav/index.html | grep -E '[0-9]{1,3}.jpg' | wc -l`
 if [[ $IMAGE_NUM_NEEDED -gt $IMAGE_NUM_ALL ]]; then
     alarm='Navigation:\nThere is NOT enough logos to use, please check ASAP.'