diff --git a/scripts/upgrade.py b/scripts/upgrade.py
index 46e727f..1345048 100755
--- a/scripts/upgrade.py
+++ b/scripts/upgrade.py
@@ -82,7 +82,7 @@ def install_command(url):
              if len(current) == 1: current = current[0] 
              else: current = "0.0.0"
              print("Upgrading from: %s -> %s" % (current, target_version))
-             perform_upgrade_command(target_version,mysql=(os.environ["SEAF_MYSQL"] or False))
+             perform_upgrade_command(target_version,mysql=("SEAF_MYSQL" in os.environ and os.environ["SEAF_MYSQL"]))
       if len(os.listdir(tmp)) != 0:
          print("Failed to unpack update")
          os.rmdir(tmp)