diff --git a/mobile/src/main/java/com/github/shadowsocks/acl/CustomRulesFragment.kt b/mobile/src/main/java/com/github/shadowsocks/acl/CustomRulesFragment.kt
index 061a76a3..64c511ce 100644
--- a/mobile/src/main/java/com/github/shadowsocks/acl/CustomRulesFragment.kt
+++ b/mobile/src/main/java/com/github/shadowsocks/acl/CustomRulesFragment.kt
@@ -439,4 +439,9 @@ class CustomRulesFragment : ToolbarFragment(), Toolbar.OnMenuItemClickListener {
         }
         else -> false
     }
+
+    override fun onDetach() {
+        undoManager.flush()
+        super.onDetach()
+    }
 }