diff --git a/sys/dev/netmap/netmap.c b/sys/dev/netmap/netmap.c
--- a/sys/dev/netmap/netmap.c
+++ b/sys/dev/netmap/netmap.c
@@ -1710,8 +1710,8 @@
 u_int
 nm_txsync_prologue(struct netmap_kring *kring, struct netmap_ring *ring)
 {
-	u_int head = ring->head; /* read only once */
-	u_int cur = ring->cur; /* read only once */
+	u_int head = NM_ACCESS_ONCE(ring->head);
+	u_int cur = NM_ACCESS_ONCE(ring->cur);
 	u_int n = kring->nkr_num_slots;
 
 	nm_prdis(5, "%s kcur %d ktail %d head %d cur %d tail %d",
@@ -1788,8 +1788,8 @@
 	 * - cur could in principle go back, however it does not matter
 	 *   because we are processing a brand new rxsync()
 	 */
-	cur = kring->rcur = ring->cur;	/* read only once */
-	head = kring->rhead = ring->head;	/* read only once */
+	cur = kring->rcur = NM_ACCESS_ONCE(ring->cur);
+	head = kring->rhead = NM_ACCESS_ONCE(ring->head);
 #if 1 /* kernel sanity checks */
 	NM_FAIL_ON(kring->nr_hwcur >= n || kring->nr_hwtail >= n);
 #endif /* kernel sanity checks */