diff --git a/sys/vm/swap_pager.c b/sys/vm/swap_pager.c
index 53ad161a86cb..b844d029e9f9 100644
--- a/sys/vm/swap_pager.c
+++ b/sys/vm/swap_pager.c
@@ -1359,7 +1359,9 @@ swap_pager_putpages(object, m, count, sync, rtvals)
 
 		cnt.v_swapout++;
 		cnt.v_swappgsout += bp->b_npages;
+		VI_LOCK(swapdev_vp);
 		swapdev_vp->v_numoutput++;
+		VI_UNLOCK(swapdev_vp);
 
 		splx(s);
 
diff --git a/sys/vm/vm_swap.c b/sys/vm/vm_swap.c
index 80766e501052..6d16e38b35de 100644
--- a/sys/vm/vm_swap.c
+++ b/sys/vm/vm_swap.c
@@ -151,7 +151,9 @@ swapdev_strategy(ap)
 			}
 			VI_UNLOCK(vp);
 		}
+		VI_LOCK(sp->sw_vp);
 		sp->sw_vp->v_numoutput++;
+		VI_UNLOCK(sp->sw_vp);
 	}
 	bp->b_vp = sp->sw_vp;
 	splx(s);