diff --git a/update_manager/policy.h b/update_manager/policy.h
index 9a7d620..8ec5c9e 100644
--- a/update_manager/policy.h
+++ b/update_manager/policy.h
@@ -30,6 +30,8 @@
 
   // Attributes pertaining to the case where update checks are allowed.
   //
+  // A target version prefix, if imposed by policy; otherwise, an empty string.
+  std::string target_version_prefix;
   // A target channel, if so imposed by policy; otherwise, an empty string.
   std::string target_channel;