Index: sys/kern/kern_umtx.c
===================================================================
--- sys/kern/kern_umtx.c
+++ sys/kern/kern_umtx.c
@@ -820,8 +820,8 @@
 		    (share == AUTO_SHARE &&
 		     VM_INHERIT_SHARE == entry->inheritance)) {
 			key->shared = 1;
-			key->info.shared.offset = entry->offset + entry->start -
-				(vm_offset_t)addr;
+			key->info.shared.offset = (vm_offset_t)addr -
+			    entry->start + entry->offset;
 			vm_object_reference(key->info.shared.object);
 		} else {
 			key->shared = 0;