diff --git a/externs/olx.js b/externs/olx.js
index 4f864f5467..8f480b4118 100644
--- a/externs/olx.js
+++ b/externs/olx.js
@@ -4235,7 +4235,8 @@ olx.source.MapQuestOptions.prototype.url;
 
 /**
  * @typedef {{projection: ol.proj.ProjectionLike,
- *     tileGrid: (ol.tilegrid.TileGrid|undefined)}}
+ *     tileGrid: (ol.tilegrid.TileGrid|undefined),
+ *     wrapX: (boolean|undefined)}}
  * @api
  */
 olx.source.TileDebugOptions;
@@ -4257,6 +4258,14 @@ olx.source.TileDebugOptions.prototype.projection;
 olx.source.TileDebugOptions.prototype.tileGrid;
 
 
+/**
+ * Whether to wrap the world horizontally. Default is `true`.
+ * @type {boolean|undefined}
+ * @api
+ */
+olx.source.TileDebugOptions.prototype.wrapX;
+
+
 /**
  * @typedef {{attributions: (Array.<ol.Attribution>|undefined),
  *     crossOrigin: (null|string|undefined),
@@ -6142,7 +6151,7 @@ olx.tilegrid.TileGridOptions;
 /**
  * Extent for the tile grid. No tiles outside this extent will be requested by
  * {@link ol.source.Tile} sources. When no `origin` or `origins` are
- * configured, the `origin` will be set to the bottom-left corner of the extent.
+ * configured, the `origin` will be set to the top-left corner of the extent.
  * @type {ol.Extent|undefined}
  * @api
  */
@@ -6189,17 +6198,6 @@ olx.tilegrid.TileGridOptions.prototype.origins;
 olx.tilegrid.TileGridOptions.prototype.resolutions;
 
 
-/**
- * Number of tile rows and columns of the grid for each zoom level. This setting
- * is only needed for tile coordinate transforms that need to work with origins
- * other than the bottom-left corner of the grid. No tiles outside this range
- * will be requested by sources. If an `extent` is also configured, it takes
- * precedence.
- * @type {Array.<ol.Size>|undefined}
- */
-olx.tilegrid.TileGridOptions.prototype.sizes;
-
-
 /**
  * Tile size. Default is `[256, 256]`.
  * @type {number|ol.Size|undefined}
@@ -6233,9 +6231,8 @@ olx.tilegrid.WMTSOptions;
 
 /**
  * Extent for the tile grid. No tiles outside this extent will be requested by
- * {@link ol.source.WMTS} sources. When no `origin` or `origins` are
- * configured, the `origin` will be calculated from the extent.
- * When no `sizes` are configured, they will be calculated from the extent.
+ * {@link ol.source.Tile} sources. When no `origin` or `origins` are
+ * configured, the `origin` will be set to the top-left corner of the extent.
  * @type {ol.Extent|undefined}
  * @api
  */
@@ -6243,19 +6240,23 @@ olx.tilegrid.WMTSOptions.prototype.extent;
 
 
 /**
- * Origin, i.e. the top-left corner of the grid.
+ * The tile grid origin, i.e. where the `x` and `y` axes meet (`[z, 0, 0]`).
+ * Tile coordinates increase from left to right and from bottom to top. If not
+ * specified, `extent` or `origins` must be provided.
  * @type {ol.Coordinate|undefined}
- * @api
+ * @api stable
  */
 olx.tilegrid.WMTSOptions.prototype.origin;
 
 
 /**
- * Origins, i.e. the top-left corners of the grid for each zoom level. The
- * length of this array needs to match the length of the
- * `resolutions` array.
+ * Tile grid origins, i.e. where the `x` and `y` axes meet (`[z, 0, 0]`), for
+ * each zoom level. If given, the array length should match the length of the
+ * `resolutions` array, i.e. each resolution can have a different origin. Tile
+ * coordinates increase from left to right and from bottom to top. If not
+ * specified, `extent` or `origin` must be provided.
  * @type {Array.<ol.Coordinate>|undefined}
- * @api
+ * @api stable
  */
 olx.tilegrid.WMTSOptions.prototype.origins;
 
@@ -6284,7 +6285,10 @@ olx.tilegrid.WMTSOptions.prototype.matrixIds;
  * here are the `TileMatrixWidth` and `TileMatrixHeight` advertised in the
  * GetCapabilities response of the WMTS, and define the grid's extent together
  * with the `origin`. An `extent` can be configured in addition, and will
- * further limit the extent for which tile requests are made by sources.
+ * further limit the extent for which tile requests are made by sources. Note
+ * that when the top-left corner of the `extent` is used as `origin` or
+ * `origins`, then the `y` value must be negative because OpenLayers tile
+ * coordinates increase from bottom to top.
  * @type {Array.<ol.Size>|undefined}
  * @api
  */
diff --git a/src/ol/source/tiledebugsource.js b/src/ol/source/tiledebugsource.js
index 59a1540f00..01d884bb8f 100644
--- a/src/ol/source/tiledebugsource.js
+++ b/src/ol/source/tiledebugsource.js
@@ -91,7 +91,8 @@ ol.source.TileDebug = function(options) {
   goog.base(this, {
     opaque: false,
     projection: options.projection,
-    tileGrid: options.tileGrid
+    tileGrid: options.tileGrid,
+    wrapX: goog.isDef(options.wrapX) ? options.wrapX : true
   });
 
 };
@@ -108,8 +109,9 @@ ol.source.TileDebug.prototype.getTile = function(z, x, y) {
   } else {
     var tileSize = ol.size.toSize(this.tileGrid.getTileSize(z));
     var tileCoord = [z, x, y];
-    var text = ol.tilecoord.toString(
-        this.getTileCoordForTileUrlFunction(tileCoord));
+    var textTileCoord = this.getTileCoordForTileUrlFunction(tileCoord);
+    var text = goog.isNull(textTileCoord) ? '' : ol.tilecoord.toString(
+        this.getTileCoordForTileUrlFunction(textTileCoord));
     var tile = new ol.DebugTile_(tileCoord, tileSize, text);
     this.tileCache.set(tileCoordKey, tile);
     return tile;