diff --git a/lib/OpenLayers/Layer/WMS.js b/lib/OpenLayers/Layer/WMS.js
index 80ce2223b1..80f74e4228 100644
--- a/lib/OpenLayers/Layer/WMS.js
+++ b/lib/OpenLayers/Layer/WMS.js
@@ -66,11 +66,11 @@ OpenLayers.Layer.WMS = OpenLayers.Class(OpenLayers.Layer.Grid, {
     
     /**
      * Property: yx
-     * {Array} Array of strings with the EPSG codes for which the axis order
-     *     is to be reversed (yx instead of xy, LatLon instead of LonLat). This
-     *     is only relevant for WMS versions >= 1.3.0.
+     * {Object} Keys in this object are EPSG codes for which the axis order
+     *     is to be reversed (yx instead of xy, LatLon instead of LonLat), with
+     *     true as value. This is only relevant for WMS versions >= 1.3.0.
      */
-    yx: ['EPSG:4326'],
+    yx: {'EPSG:4326': true},
     
     /**
      * Constructor: OpenLayers.Layer.WMS
@@ -166,8 +166,7 @@ OpenLayers.Layer.WMS = OpenLayers.Class(OpenLayers.Layer.Grid, {
      */
     reverseAxisOrder: function() {
         return (parseFloat(this.params.VERSION) >= 1.3 && 
-            OpenLayers.Util.indexOf(this.yx, 
-            this.map.getProjectionObject().getCode()) !== -1)
+            !!this.yx[this.map.getProjectionObject().getCode()]);
     },
     
     /**