Index: vm_map.c
===================================================================
--- vm_map.c
+++ vm_map.c
@@ -2192,7 +2192,10 @@
 	 * entry BEFORE this one, so that this entry has the specified
 	 * starting address.
 	 */
-	vm_map_simplify_entry(map, entry);
+	KASSERT((entry->eflags & MAP_ENTRY_NOMERGE_MASK) != 0 ||
+	    (!vm_map_mergeable_neighbors(entry->prev, entry) &&
+	    !vm_map_mergeable_neighbors(entry, entry->next)),
+	    ("_vm_map_clip_begin: entry can be simplified"));
 	vm_map_entry_charge_object(map, entry);
 	new_entry = vm_map_entry_create(map);
 	*new_entry = *entry;