From 3b83f666c103b43abc8878ecd9bf79d6db97c409 Mon Sep 17 00:00:00 2001
From: Tim Schaub <tim.schaub@gmail.com>
Date: Thu, 13 Apr 2017 05:46:46 -0600
Subject: [PATCH] Add notes about new duplicate layer behavior

---
 changelog/upgrade-notes.md | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/changelog/upgrade-notes.md b/changelog/upgrade-notes.md
index 79eadf1cbf..91ffb6456e 100644
--- a/changelog/upgrade-notes.md
+++ b/changelog/upgrade-notes.md
@@ -2,6 +2,18 @@
 
 ### Next release
 
+#### Adding duplicate layers to a map throws
+
+Previously, you could do this:
+```js
+map.addLayer(layer);
+map.addLayer(layer);
+```
+
+However, after adding a duplicate layer, things failed if you tried to remove that layer.
+
+Now, `map.addLayer()` throws if you try adding a layer that has already been added to the map.
+
 #### Simpler `constrainResolution` configuration
 
 The `constrainResolution` configuration for `ol.interaction.PinchZoom` and `ol.interaction.MouseWheelZoom`