diff --git a/src/ol/renderer/Map.js b/src/ol/renderer/Map.js
index dc7c63ffa2..b35fd3d667 100644
--- a/src/ol/renderer/Map.js
+++ b/src/ol/renderer/Map.js
@@ -336,7 +336,7 @@ MapRenderer.prototype.scheduleRemoveUnusedLayerRenderers = function(frameState)
  * @param {ol.LayerState} state2 Second layer state.
  * @return {number} The zIndex difference.
  */
-MapRenderer.sortByZIndex = function(state1, state2) {
+export function sortByZIndex(state1, state2) {
   return state1.zIndex - state2.zIndex;
-};
+}
 export default MapRenderer;
diff --git a/src/ol/renderer/canvas/Map.js b/src/ol/renderer/canvas/Map.js
index 2bf44fd300..4bdab957e6 100644
--- a/src/ol/renderer/canvas/Map.js
+++ b/src/ol/renderer/canvas/Map.js
@@ -13,7 +13,7 @@ import RenderEvent from '../../render/Event.js';
 import RenderEventType from '../../render/EventType.js';
 import _ol_render_canvas_ from '../../render/canvas.js';
 import CanvasImmediateRenderer from '../../render/canvas/Immediate.js';
-import MapRenderer from '../Map.js';
+import MapRenderer, {sortByZIndex} from '../Map.js';
 import RendererType from '../Type.js';
 import SourceState from '../../source/State.js';
 
@@ -166,7 +166,7 @@ CanvasMapRenderer.prototype.renderFrame = function(frameState) {
   this.dispatchComposeEvent_(RenderEventType.PRECOMPOSE, frameState);
 
   const layerStatesArray = frameState.layerStatesArray;
-  stableSort(layerStatesArray, MapRenderer.sortByZIndex);
+  stableSort(layerStatesArray, sortByZIndex);
 
   if (rotation) {
     context.save();
diff --git a/src/ol/renderer/webgl/Map.js b/src/ol/renderer/webgl/Map.js
index d3aefcb158..ec9a0fd90e 100644
--- a/src/ol/renderer/webgl/Map.js
+++ b/src/ol/renderer/webgl/Map.js
@@ -12,7 +12,7 @@ import Layer from '../../layer/Layer.js';
 import RenderEvent from '../../render/Event.js';
 import RenderEventType from '../../render/EventType.js';
 import WebGLImmediateRenderer from '../../render/webgl/Immediate.js';
-import MapRenderer from '../Map.js';
+import MapRenderer, {sortByZIndex} from '../Map.js';
 import RendererType from '../Type.js';
 import SourceState from '../../source/State.js';
 import LRUCache from '../../structs/LRUCache.js';
@@ -444,7 +444,7 @@ WebGLMapRenderer.prototype.renderFrame = function(frameState) {
   /** @type {Array.<ol.LayerState>} */
   const layerStatesToDraw = [];
   const layerStatesArray = frameState.layerStatesArray;
-  stableSort(layerStatesArray, MapRenderer.sortByZIndex);
+  stableSort(layerStatesArray, sortByZIndex);
 
   const viewResolution = frameState.viewState.resolution;
   let i, ii, layerRenderer, layerState;
diff --git a/test/spec/ol/layer/group.test.js b/test/spec/ol/layer/group.test.js
index df1020af09..fbe7c6a950 100644
--- a/test/spec/ol/layer/group.test.js
+++ b/test/spec/ol/layer/group.test.js
@@ -5,7 +5,7 @@ import * as _ol_extent_ from '../../../../src/ol/extent.js';
 import LayerGroup from '../../../../src/ol/layer/Group.js';
 import Layer from '../../../../src/ol/layer/Layer.js';
 import {assign} from '../../../../src/ol/obj.js';
-import MapRenderer from '../../../../src/ol/renderer/Map.js';
+import {sortByZIndex} from '../../../../src/ol/renderer/Map.js';
 import Source from '../../../../src/ol/source/Source.js';
 
 
@@ -451,7 +451,7 @@ describe('ol.layer.Group', function() {
 
       const layerStatesArray = layerGroup.getLayerStatesArray();
       const initialArray = layerStatesArray.slice();
-      stableSort(layerStatesArray, MapRenderer.sortByZIndex);
+      stableSort(layerStatesArray, sortByZIndex);
       expect(layerStatesArray[0]).to.eql(initialArray[0]);
       expect(layerStatesArray[1]).to.eql(initialArray[1]);
 
@@ -479,7 +479,7 @@ describe('ol.layer.Group', function() {
 
       const layerStatesArray = layerGroup.getLayerStatesArray();
       const initialArray = layerStatesArray.slice();
-      stableSort(layerStatesArray, MapRenderer.sortByZIndex);
+      stableSort(layerStatesArray, sortByZIndex);
       expect(layerStatesArray[0]).to.eql(initialArray[3]);
       expect(layerStatesArray[1]).to.eql(initialArray[0]);
       expect(layerStatesArray[2]).to.eql(initialArray[2]);