diff --git a/coregrind/m_syswrap/syswrap-xen.c b/coregrind/m_syswrap/syswrap-xen.c
index e962a4701..645b00111 100644
--- a/coregrind/m_syswrap/syswrap-xen.c
+++ b/coregrind/m_syswrap/syswrap-xen.c
@@ -124,7 +124,8 @@ PRE(memory_op)
                     (Addr)ARG2, sizeof(vki_xen_domid_t));
        break;
 
-   case VKI_XENMEM_machphys_mfn_list: {
+   case VKI_XENMEM_machphys_mfn_list:
+   case VKI_XENMEM_machphys_compat_mfn_list: {
        struct vki_xen_machphys_mfn_list *arg =
            (struct vki_xen_machphys_mfn_list *)ARG2;
        PRE_MEM_READ("XENMEM_machphys_mfn_list max_extents",
@@ -1207,7 +1208,8 @@ POST(memory_op)
       break;
    }
 
-   case VKI_XENMEM_machphys_mfn_list: {
+   case VKI_XENMEM_machphys_mfn_list:
+   case VKI_XENMEM_machphys_compat_mfn_list: {
        struct vki_xen_machphys_mfn_list *arg =
            (struct vki_xen_machphys_mfn_list *)ARG2;
        POST_MEM_WRITE((Addr)&arg->nr_extents, sizeof(arg->nr_extents));
diff --git a/include/vki/vki-xen-memory.h b/include/vki/vki-xen-memory.h
index 2690c60c2..abb756fc7 100644
--- a/include/vki/vki-xen-memory.h
+++ b/include/vki/vki-xen-memory.h
@@ -22,6 +22,7 @@
 #define VKI_XENMEM_get_sharing_shared_pages   19
 #define VKI_XENMEM_access_op                  21
 #define VKI_XENMEM_claim_pages                24
+#define VKI_XENMEM_machphys_compat_mfn_list   25
 
 struct vki_xen_memory_map {
     unsigned int nr_entries;