diff --git a/src/ol/source/BingMaps.js b/src/ol/source/BingMaps.js
index 3b0e8d3e06..5bb46b29e0 100644
--- a/src/ol/source/BingMaps.js
+++ b/src/ol/source/BingMaps.js
@@ -83,9 +83,8 @@ inherits(BingMaps, TileImage);
  * Terms Of Use.
  * @const
  * @type {string}
- * @api
  */
-BingMaps.TOS_ATTRIBUTION = '<a class="ol-attribution-bing-tos" ' +
+const TOS_ATTRIBUTION = '<a class="ol-attribution-bing-tos" ' +
       'href="https://www.microsoft.com/maps/product/terms.html">' +
       'Terms of Use</a>';
 
@@ -197,7 +196,7 @@ BingMaps.prototype.handleImageryMetadataResponse = function(response) {
         }
       });
 
-      attributions.push(BingMaps.TOS_ATTRIBUTION);
+      attributions.push(TOS_ATTRIBUTION);
       return attributions;
     });
   }