diff --git a/src/qemu/qemu_domain.h b/src/qemu/qemu_domain.h
index abc3c7158d..f3c6bb3390 100644
--- a/src/qemu/qemu_domain.h
+++ b/src/qemu/qemu_domain.h
@@ -154,6 +154,14 @@ struct _qemuDomainObjPrivate {
 
     bool fakeReboot;
     bool pausedShutdown;
+    /* allowReboot:
+     *
+     * Unused with new QEMU versions which have QEMU_CAPS_SET_ACTION.
+     *
+     * Otherwise if it's set to VIR_TRISTATE_BOOL_YES, QEMU was started with
+     * -no-shutdown, and if set to VIR_TRISTATE_BOOL_NO qemu was started with
+     * -no-reboot instead.
+     */
     virTristateBool allowReboot;
 
     int jobs_queued;