diff --git a/drivers/iommu/iommufd/driver.c b/drivers/iommu/iommufd/driver.c
index cd9ab2cf6a5f4df8bc33161d8fe0cf8f2088f323..418fba10688a0af8c905ba28ab8a06bec6d5d699 100644
--- a/drivers/iommu/iommufd/driver.c
+++ b/drivers/iommu/iommufd/driver.c
@@ -161,8 +161,8 @@ int iommufd_viommu_report_event(struct iommufd_viommu *viommu,
 		vevent = &veventq->lost_events_header;
 		goto out_set_header;
 	}
-	memcpy(vevent->event_data, event_data, data_len);
 	vevent->data_len = data_len;
+	memcpy(vevent->event_data, event_data, data_len);
 	veventq->num_events++;
 
 out_set_header:
diff --git a/drivers/iommu/iommufd/iommufd_private.h b/drivers/iommu/iommufd/iommufd_private.h
index 627f9b78483a0ea874ca22f65b9466318c869814..85d0843ed07b0ba6ead4de74d505000bc12cd474 100644
--- a/drivers/iommu/iommufd/iommufd_private.h
+++ b/drivers/iommu/iommufd/iommufd_private.h
@@ -614,7 +614,6 @@ struct iommufd_veventq {
 	struct iommufd_eventq common;
 	struct iommufd_viommu *viommu;
 	struct list_head node; /* for iommufd_viommu::veventqs */
-	struct iommufd_vevent lost_events_header;
 
 	enum iommu_veventq_type type;
 	unsigned int depth;
@@ -622,6 +621,9 @@ struct iommufd_veventq {
 	/* Use common.lock for protection */
 	u32 num_events;
 	u32 sequence;
+
+	/* Must be last as it ends in a flexible-array member. */
+	struct iommufd_vevent lost_events_header;
 };
 
 static inline struct iommufd_veventq *