Index: sbin/swapon/swapon.c
===================================================================
--- sbin/swapon/swapon.c
+++ sbin/swapon/swapon.c
@@ -761,8 +761,8 @@
 	} else
 		errx(1, "%s has an invalid file type", name);
 	/* Trim the device. */
-	ioarg[0] = 0;
-	ioarg[1] = sz;
+	ioarg[0] = BSD_LABEL_SIZE;
+	ioarg[1] = sz - BSD_LABEL_SIZE;
 	if (ioctl(fd, DIOCGDELETE, ioarg) != 0)
 		warn("ioctl(DIOCGDELETE)");
 
Index: sys/vm/swap_pager.c
===================================================================
--- sys/vm/swap_pager.c
+++ sys/vm/swap_pager.c
@@ -2298,10 +2298,10 @@
 
 	sp->sw_blist = blist_create(nblks, M_WAITOK);
 	/*
-	 * Do not free the first two block in order to avoid overwriting
+	 * Do not free the first blocks in order to avoid overwriting
 	 * any bsd label at the front of the partition
 	 */
-	blist_free(sp->sw_blist, 2, nblks - 2);
+	blist_free(sp->sw_blist, BSD_LABEL_SIZE, nblks - BSD_LABEL_SIZE);
 
 	dvbase = 0;
 	mtx_lock(&sw_dev_mtx);
@@ -2319,7 +2319,7 @@
 	sp->sw_end = dvbase + nblks;
 	TAILQ_INSERT_TAIL(&swtailq, sp, sw_list);
 	nswapdev++;
-	swap_pager_avail += nblks - 2;
+	swap_pager_avail += nblks - BSD_LABEL_SIZE;
 	swap_total += nblks;
 	swapon_check_swzone();
 	swp_sizecheck();
Index: sys/vm/vm_param.h
===================================================================
--- sys/vm/vm_param.h
+++ sys/vm/vm_param.h
@@ -122,6 +122,10 @@
 #endif	/* !SMP */
 #endif	/* !PA_LOCK_COUNT */
 
+#ifndef BSD_LABEL_SIZE
+#define BSD_LABEL_SIZE 2
+#endif BSD_LABEL_SIZE
+
 #ifndef KSTACK_MAX_PAGES
 #define KSTACK_MAX_PAGES 32
 #endif