diff --git a/sys/vm/vm_page.c b/sys/vm/vm_page.c
index 696f4eebfeff..0242fe54f6fb 100644
--- a/sys/vm/vm_page.c
+++ b/sys/vm/vm_page.c
@@ -1200,7 +1200,7 @@ vm_page_replace(vm_page_t mnew, vm_object_t object, vm_pindex_t pindex)
 
 	mnew->object = object;
 	mnew->pindex = pindex;
-	mold = vm_radix_replace(&object->rtree, mnew, pindex);
+	mold = vm_radix_replace(&object->rtree, mnew);
 	KASSERT(mold->queue == PQ_NONE,
 	    ("vm_page_replace: mold is on a paging queue"));
 
diff --git a/sys/vm/vm_radix.c b/sys/vm/vm_radix.c
index ff311b2d5b55..7c6f7fa40328 100644
--- a/sys/vm/vm_radix.c
+++ b/sys/vm/vm_radix.c
@@ -788,20 +788,18 @@ vm_radix_reclaim_allnodes(struct vm_radix *rtree)
 }
 
 /*
- * Replace an existing page into the trie with another one.
- * Panics if the replacing page is not present or if the new page has an
- * invalid key.
+ * Replace an existing page in the trie with another one.
+ * Panics if there is not an old page in the trie at the new page's index.
  */
 vm_page_t
-vm_radix_replace(struct vm_radix *rtree, vm_page_t newpage, vm_pindex_t index)
+vm_radix_replace(struct vm_radix *rtree, vm_page_t newpage)
 {
 	struct vm_radix_node *rnode;
 	vm_page_t m;
+	vm_pindex_t index;
 	int slot;
 
-	KASSERT(newpage->pindex == index, ("%s: newpage index invalid",
-	    __func__));
-
+	index = newpage->pindex;
 	rnode = vm_radix_getroot(rtree);
 	if (rnode == NULL)
 		panic("%s: replacing page on an empty trie", __func__);
diff --git a/sys/vm/vm_radix.h b/sys/vm/vm_radix.h
index 4491860027b8..63d27d4f088f 100644
--- a/sys/vm/vm_radix.h
+++ b/sys/vm/vm_radix.h
@@ -43,8 +43,7 @@ vm_page_t	vm_radix_lookup_ge(struct vm_radix *rtree, vm_pindex_t index);
 vm_page_t	vm_radix_lookup_le(struct vm_radix *rtree, vm_pindex_t index);
 void		vm_radix_reclaim_allnodes(struct vm_radix *rtree);
 void		vm_radix_remove(struct vm_radix *rtree, vm_pindex_t index);
-vm_page_t	vm_radix_replace(struct vm_radix *rtree, vm_page_t newpage,
-		    vm_pindex_t index);
+vm_page_t	vm_radix_replace(struct vm_radix *rtree, vm_page_t newpage);
 
 #endif /* _KERNEL */
 #endif /* !_VM_RADIX_H_ */