diff --git a/xen/common/event_fifo.c b/xen/common/event_fifo.c
index 27ab3a1c3f..2037b24196 100644
--- a/xen/common/event_fifo.c
+++ b/xen/common/event_fifo.c
@@ -21,6 +21,14 @@
 
 #include <public/event_channel.h>
 
+union evtchn_fifo_lastq {
+    uint32_t raw;
+    struct {
+        uint8_t last_priority;
+        uint16_t last_vcpu_id;
+    };
+};
+
 static inline event_word_t *evtchn_fifo_word_from_port(const struct domain *d,
                                                        unsigned int port)
 {
@@ -65,16 +73,18 @@ static struct evtchn_fifo_queue *lock_old_queue(const struct domain *d,
     struct vcpu *v;
     struct evtchn_fifo_queue *q, *old_q;
     unsigned int try;
+    union evtchn_fifo_lastq lastq;
 
     for ( try = 0; try < 3; try++ )
     {
-        v = d->vcpu[evtchn->last_vcpu_id];
-        old_q = &v->evtchn_fifo->queue[evtchn->last_priority];
+        lastq.raw = read_atomic(&evtchn->fifo_lastq);
+        v = d->vcpu[lastq.last_vcpu_id];
+        old_q = &v->evtchn_fifo->queue[lastq.last_priority];
 
         spin_lock_irqsave(&old_q->lock, *flags);
 
-        v = d->vcpu[evtchn->last_vcpu_id];
-        q = &v->evtchn_fifo->queue[evtchn->last_priority];
+        v = d->vcpu[lastq.last_vcpu_id];
+        q = &v->evtchn_fifo->queue[lastq.last_priority];
 
         if ( old_q == q )
             return old_q;
@@ -225,8 +235,11 @@ static void evtchn_fifo_set_pending(struct vcpu *v, struct evtchn *evtchn)
         /* Moved to a different queue? */
         if ( old_q != q )
         {
-            evtchn->last_vcpu_id = v->vcpu_id;
-            evtchn->last_priority = q->priority;
+            union evtchn_fifo_lastq lastq = { };
+
+            lastq.last_vcpu_id = v->vcpu_id;
+            lastq.last_priority = q->priority;
+            write_atomic(&evtchn->fifo_lastq, lastq.raw);
 
             spin_unlock_irqrestore(&old_q->lock, flags);
             spin_lock_irqsave(&q->lock, flags);
diff --git a/xen/include/xen/sched.h b/xen/include/xen/sched.h
index 89a9df5a63..8bf1b90261 100644
--- a/xen/include/xen/sched.h
+++ b/xen/include/xen/sched.h
@@ -115,8 +115,7 @@ struct evtchn
 #ifndef NDEBUG
     u8 old_state;      /* State when taking lock in write mode. */
 #endif
-    u8 last_priority;
-    u16 last_vcpu_id;
+    u32 fifo_lastq;    /* Data for fifo events identifying last queue. */
 #ifdef CONFIG_XSM
     union {
 #ifdef XSM_NEED_GENERIC_EVTCHN_SSID