diff --git a/include/xen/interface/memory.h b/include/xen/interface/memory.h
index eac3ce153719..8d4efc1cc64a 100644
--- a/include/xen/interface/memory.h
+++ b/include/xen/interface/memory.h
@@ -163,6 +163,9 @@ struct xen_add_to_physmap {
     /* Which domain to change the mapping for. */
     domid_t domid;
 
+    /* Number of pages to go through for gmfn_range */
+    uint16_t    size;
+
     /* Source mapping space. */
 #define XENMAPSPACE_shared_info 0 /* shared info page */
 #define XENMAPSPACE_grant_table 1 /* grant table page */