Index: head/sys/vm/vm_object.c
===================================================================
--- head/sys/vm/vm_object.c
+++ head/sys/vm/vm_object.c
@@ -2142,8 +2142,9 @@
 	next_size >>= PAGE_SHIFT;
 	next_pindex = OFF_TO_IDX(prev_offset) + prev_size;
 
-	if ((prev_object->ref_count > 1) &&
-	    (prev_object->size != next_pindex)) {
+	if (prev_object->ref_count > 1 &&
+	    prev_object->size != next_pindex &&
+	    (prev_object->flags & OBJ_ONEMAPPING) == 0) {
 		VM_OBJECT_WUNLOCK(prev_object);
 		return (FALSE);
 	}