diff --git a/sys/vm/swap_pager.c b/sys/vm/swap_pager.c
--- a/sys/vm/swap_pager.c
+++ b/sys/vm/swap_pager.c
@@ -482,7 +482,8 @@
 /*
  * Metadata functions
  */
-static daddr_t swp_pager_meta_build(vm_object_t, vm_pindex_t, daddr_t);
+static void swp_pager_meta_build(vm_object_t object, vm_pindex_t pindex,
+    daddr_t swapblk, daddr_t *s_free, daddr_t *n_free);
 static void swp_pager_meta_free(vm_object_t, vm_pindex_t, vm_pindex_t);
 static void swp_pager_meta_transfer(vm_object_t src, vm_object_t dst,
     vm_pindex_t pindex, vm_pindex_t count);
@@ -998,7 +999,7 @@
 int
 swap_pager_reserve(vm_object_t object, vm_pindex_t start, vm_pindex_t size)
 {
-	daddr_t addr, blk, n_free, s_free;
+	daddr_t blk, n_free, s_free;
 	vm_pindex_t i, j;
 	int n;
 
@@ -1013,11 +1014,8 @@
 			return (-1);
 		}
 		for (j = 0; j < n; ++j) {
-			addr = swp_pager_meta_build(object,
-			    start + i + j, blk + j);
-			if (addr != SWAPBLK_NONE)
-				swp_pager_update_freerange(&s_free, &n_free,
-				    addr);
+			swp_pager_meta_build(object, start + i + j, blk + j,
+			    &s_free, &n_free);
 		}
 	}
 	swp_pager_freeswapspace(s_free, n_free);
@@ -1029,8 +1027,6 @@
 swp_pager_xfer_source(vm_object_t srcobject, vm_object_t dstobject,
     vm_pindex_t pindex, daddr_t addr)
 {
-	daddr_t dstaddr __diagused;
-
 	KASSERT((srcobject->flags & OBJ_SWAP) != 0,
 	    ("%s: srcobject not swappable", __func__));
 	KASSERT((dstobject->flags & OBJ_SWAP) != 0,
@@ -1046,9 +1042,7 @@
 	 * swp_pager_meta_build() can sleep.
 	 */
 	VM_OBJECT_WUNLOCK(srcobject);
-	dstaddr = swp_pager_meta_build(dstobject, pindex, addr);
-	KASSERT(dstaddr == SWAPBLK_NONE,
-	    ("Unexpected destination swapblk"));
+	swp_pager_meta_build(dstobject, pindex, addr, NULL, NULL);
 	VM_OBJECT_WLOCK(srcobject);
 
 	return (true);
@@ -1474,7 +1468,7 @@
     int flags, int *rtvals)
 {
 	struct buf *bp;
-	daddr_t addr, blk, n_free, s_free;
+	daddr_t blk, n_free, s_free;
 	vm_page_t mreq;
 	int i, j, n;
 	bool async;
@@ -1520,11 +1514,8 @@
 		for (j = 0; j < n; ++j) {
 			mreq = ma[i + j];
 			vm_page_aflag_clear(mreq, PGA_SWAP_FREE);
-			addr = swp_pager_meta_build(mreq->object, mreq->pindex,
-			    blk + j);
-			if (addr != SWAPBLK_NONE)
-				swp_pager_update_freerange(&s_free, &n_free,
-				    addr);
+			swp_pager_meta_build(mreq->object, mreq->pindex,
+			    blk + j, &s_free, &n_free);
 			MPASS(mreq->dirty == VM_PAGE_BITS_ALL);
 			mreq->oflags |= VPO_SWAPINPROG;
 		}
@@ -2013,10 +2004,11 @@
  *
  *	The specified swapblk is added to the object's swap metadata.  If
  *	the swapblk is not valid, it is freed instead.  Any previously
- *	assigned swapblk is returned.
+ *	assigned swapblk is added to the provided freerange.
  */
-static daddr_t
-swp_pager_meta_build(vm_object_t object, vm_pindex_t pindex, daddr_t swapblk)
+static void
+swp_pager_meta_build(vm_object_t object, vm_pindex_t pindex, daddr_t swapblk,
+    daddr_t *s_free, daddr_t *n_free)
 {
 	static volatile int swblk_zone_exhausted, swpctrie_zone_exhausted;
 	struct swblk *sb, *sb1;
@@ -2030,7 +2022,7 @@
 	sb = SWAP_PCTRIE_LOOKUP(&object->un_pager.swp.swp_blks, rdpi);
 	if (sb == NULL) {
 		if (swapblk == SWAPBLK_NONE)
-			return (SWAPBLK_NONE);
+			return;
 		for (;;) {
 			sb = uma_zalloc(swblk_zone, M_NOWAIT | (curproc ==
 			    pageproc ? M_USE_RESERVE : 0));
@@ -2107,7 +2099,12 @@
 	 */
 	if (swapblk == SWAPBLK_NONE)
 		swp_pager_free_empty_swblk(object, sb);
-	return (prev_swapblk);
+
+	if (prev_swapblk != SWAPBLK_NONE) {
+		KASSERT(s_free != NULL && n_free != NULL,
+		    ("Unexpected previously-assigned swapblk"));
+		swp_pager_update_freerange(s_free, n_free, prev_swapblk);
+	}
 }
 
 /*