diff --git a/debian/postinst b/debian/postinst
index 26f68c8..52d967b 100755
--- a/debian/postinst
+++ b/debian/postinst
@@ -3,14 +3,15 @@ set -e
 
 case "$1" in
     configure)
-        echo "正在安装系统依赖 (aria2 + p7zip-full) ..."
-        apt-get install -y aria2 p7zip-full >/dev/null 2>&1 || true
+        echo "正在安装系统依赖 (aria2 + p7zip-full + python3-venv) ..."
+        apt-get install -y aria2 p7zip-full python3-venv >/dev/null 2>&1 || true
         P=/usr/share/7z-encrypt/.venv
         if [ ! -x "$P/bin/python" ]; then
             echo "正在创建 7z-encrypt 运行环境 (venv + cryptography/tqdm) ..."
             python3 -m venv "$P"
             "$P/bin/pip" install --quiet --upgrade pip || true
-            "$P/bin/pip" install --quiet cryptography tqdm
+            "$P/bin/pip" install --quiet cryptography tqdm \
+                || "$P/bin/pip" install --quiet -i https://pypi.tuna.tsinghua.edu.cn/simple cryptography tqdm
         fi
         ;;
 esac