diff --git a/src/objectliterals.exports b/src/objectliterals.exports
index 0e5d215c37..65508a2711 100644
--- a/src/objectliterals.exports
+++ b/src/objectliterals.exports
@@ -122,6 +122,7 @@
 @exportObjectLiteralProperty ol.source.SingleImageWMSOptions.extent ol.Extent|undefined
 @exportObjectLiteralProperty ol.source.SingleImageWMSOptions.params Object.<string,*>
 @exportObjectLiteralProperty ol.source.SingleImageWMSOptions.projection ol.ProjectionLike
+@exportObjectLiteralProperty ol.source.SingleImageWMSOptions.ratio number|undefined
 @exportObjectLiteralProperty ol.source.SingleImageWMSOptions.resolutions Array.<number>|undefined
 @exportObjectLiteralProperty ol.source.SingleImageWMSOptions.url string|undefined
 
diff --git a/src/ol/source/singleimagewmssource.js b/src/ol/source/singleimagewmssource.js
index 211abdbd36..f79591d67f 100644
--- a/src/ol/source/singleimagewmssource.js
+++ b/src/ol/source/singleimagewmssource.js
@@ -34,11 +34,11 @@ ol.source.SingleImageWMS = function(options) {
   this.image_ = null;
 
   /**
-   * FIXME configurable?
    * @private
    * @type {number}
    */
-  this.ratio_ = 1.5;
+  this.ratio_ = goog.isDef(options.ratio) ?
+      options.ratio : 1.5;
 
 };
 goog.inherits(ol.source.SingleImageWMS, ol.source.ImageSource);