diff --git a/worldedit/cuboid.lua b/worldedit/cuboid.lua
index f9a647f..e8160ae 100644
--- a/worldedit/cuboid.lua
+++ b/worldedit/cuboid.lua
@@ -64,6 +64,8 @@ worldedit.cuboid_shift = function(name, axis, amount)
 		return false, "undefined cuboid"
 	end
 
+	assert(not rawequal(pos1, pos2)) -- vectors must not alias
+
 	if axis == 'x' then
 		worldedit.pos1[name].x = pos1.x + amount
 		worldedit.pos2[name].x = pos2.x + amount
diff --git a/worldedit_commands/wand.lua b/worldedit_commands/wand.lua
index b3fdcef..4952187 100644
--- a/worldedit_commands/wand.lua
+++ b/worldedit_commands/wand.lua
@@ -34,7 +34,7 @@ minetest.register_tool(":worldedit:wand", {
 			local entity = pointed_thing.ref:get_luaentity()
 			if entity and entity.name == "worldedit:pos2" then
 				-- set pos1 = pos2
-				worldedit.pos1[name] = worldedit.pos2[name]
+				worldedit.pos1[name] = vector.copy(worldedit.pos2[name])
 				worldedit.mark_pos1(name)
 			end
 		end
@@ -59,7 +59,7 @@ minetest.register_tool(":worldedit:wand", {
 		local entity = pointed_thing.ref:get_luaentity()
 		if entity and entity.name == "worldedit:pos1" then
 			-- set pos2 = pos1
-			worldedit.pos2[name] = worldedit.pos1[name]
+			worldedit.pos2[name] = vector.copy(worldedit.pos1[name])
 			worldedit.mark_pos2(name)
 		end
 		return itemstack -- nothing consumed, nothing changed