diff --git a/src/core/dbus-unit.c b/src/core/dbus-unit.c
index ca81f6acc7..968166ee60 100644
--- a/src/core/dbus-unit.c
+++ b/src/core/dbus-unit.c
@@ -676,7 +676,7 @@ const sd_bus_vtable bus_unit_vtable[] = {
         SD_BUS_PROPERTY("SuccessActionExitStatus", "i", bus_property_get_int, offsetof(Unit, success_action_exit_status), SD_BUS_VTABLE_PROPERTY_CONST),
         SD_BUS_PROPERTY("RebootArgument", "s", NULL, offsetof(Unit, reboot_arg), SD_BUS_VTABLE_PROPERTY_CONST),
         SD_BUS_PROPERTY("InvocationID", "ay", bus_property_get_id128, offsetof(Unit, invocation_id), SD_BUS_VTABLE_PROPERTY_EMITS_CHANGE),
-        SD_BUS_PROPERTY("CollectMode", "s", property_get_collect_mode, offsetof(Unit, collect_mode), 0),
+        SD_BUS_PROPERTY("CollectMode", "s", property_get_collect_mode, offsetof(Unit, collect_mode), SD_BUS_VTABLE_PROPERTY_CONST),
         SD_BUS_PROPERTY("Refs", "as", property_get_refs, 0, 0),
 
         SD_BUS_METHOD("Start", "s", "o", method_start, SD_BUS_VTABLE_UNPRIVILEGED),