diff --git a/externs/olx.js b/externs/olx.js
index a0dbe05eb6..c1c2a45007 100644
--- a/externs/olx.js
+++ b/externs/olx.js
@@ -1470,8 +1470,8 @@ olx.format;
 
 
 /**
- * @typedef {{dataProjection: (ol.proj.ProjectionLike|undefined),
- *     featureProjection: (ol.proj.ProjectionLike|undefined)}}
+ * @typedef {{dataProjection: ol.proj.ProjectionLike,
+ *     featureProjection: ol.proj.ProjectionLike}}
  * @api
  */
 olx.format.ReadOptions;
@@ -1483,7 +1483,7 @@ olx.format.ReadOptions;
  * the format is assigned (where set). If the projection can not be derived from
  * the data and if no `defaultDataProjection` is set for a format, the features
  * will not be reprojected.
- * @type {ol.proj.ProjectionLike|undefined}
+ * @type {ol.proj.ProjectionLike}
  * @api stable
  */
 olx.format.ReadOptions.prototype.dataProjection;
@@ -1492,14 +1492,14 @@ olx.format.ReadOptions.prototype.dataProjection;
 /**
  * Projection of the feature geometries created by the format reader. If not
  * provided, features will be returned in the `dataProjection`.
- * @type {ol.proj.ProjectionLike|undefined}
+ * @type {ol.proj.ProjectionLike}
  * @api stable
  */
 olx.format.ReadOptions.prototype.featureProjection;
 
 
 /**
- * @typedef {{dataProjection: (ol.proj.ProjectionLike|undefined),
+ * @typedef {{dataProjection: ol.proj.ProjectionLike,
  *     featureProjection: ol.proj.ProjectionLike}}
  * @api
  */
@@ -1511,7 +1511,7 @@ olx.format.WriteOptions;
  * `defaultDataProjection` of the format is assigned (where set). If no
  * `defaultDataProjection` is set for a format, the features will be returned
  * in the `featureProjection`.
- * @type {ol.proj.ProjectionLike|undefined}
+ * @type {ol.proj.ProjectionLike}
  * @api stable
  */
 olx.format.WriteOptions.prototype.dataProjection;