diff --git a/pub.sh b/pub.sh
index 211dda1..b5ee02d 100755
--- a/pub.sh
+++ b/pub.sh
@@ -4,4 +4,4 @@ set -e
 BASE_URL=${MIRROR_BASE_URL:-"https://mirrors.tuna.tsinghua.edu.cn/dart-pub"}
 UPSTREAM_URL=${TUNASYNC_UPSTREAM_URL:-"https://pub.dartlang.org/api"}
 
-/pub-cache/bin/pub_mirror --upstream $UPSTREAM_URL --verbose --connections 10 --concurrency 100 "$TUNASYNC_WORKING_DIR" "$BASE_URL"
+/pub-cache/bin/pub_mirror --upstream $UPSTREAM_URL --verbose --connections 1 --concurrency 10 "$TUNASYNC_WORKING_DIR" "$BASE_URL"