diff --git a/xen/common/ioreq.c b/xen/common/ioreq.c
index de3066a0ba..07572a5c32 100644
--- a/xen/common/ioreq.c
+++ b/xen/common/ioreq.c
@@ -29,6 +29,7 @@
 #include <xen/trace.h>
 #include <xen/vpci.h>
 
+#include <asm/guest_atomics.h>
 #include <asm/ioreq.h>
 
 #include <public/hvm/ioreq.h>
@@ -1185,7 +1186,7 @@ static int ioreq_send_buffered(struct ioreq_server *s, ioreq_t *p)
 
         new.read_pointer = old.read_pointer - n * IOREQ_BUFFER_SLOT_NUM;
         new.write_pointer = old.write_pointer - n * IOREQ_BUFFER_SLOT_NUM;
-        cmpxchg(&pg->ptrs.full, old.full, new.full);
+        guest_cmpxchg64(s->emulator, &pg->ptrs.full, old.full, new.full);
     }
 
     notify_via_xen_event_channel(d, s->bufioreq_evtchn);