diff --git a/examples/wms-custom-proj.js b/examples/wms-custom-proj.js
index 4288518051..087be33acb 100644
--- a/examples/wms-custom-proj.js
+++ b/examples/wms-custom-proj.js
@@ -20,7 +20,9 @@ var projection = ol.proj.addProjection({
 // Proj4js provides transform functions between its configured projections.
 // The transform is needed for the ScaleLine control. Otherwise this example
 // would also work without transform functions.
-ol.proj.addCoordinateTransforms('EPSG:4326', projection, proj4('EPSG:21781'));
+var transform = proj4('EPSG:21781');
+ol.proj.addCoordinateTransforms('EPSG:4326', projection, transform.forward,
+    transform.inverse);
 
 var extent = [420000, 30000, 900000, 350000];
 var layers = [
diff --git a/externs/olx.js b/externs/olx.js
index 33cf67a020..59f641f951 100644
--- a/externs/olx.js
+++ b/externs/olx.js
@@ -274,33 +274,6 @@ olx.OverlayOptions.prototype.stopEvent;
 olx.OverlayOptions.prototype.insertFirst;
 
 
-/**
- * Object literal with forward and inverse coordinate transforms.
- * @typedef {{forward: function(ol.Coordinate): ol.Coordinate,
- *     inverse: function(ol.Coordinate): ol.Coordinate}}
- * @api
- */
-olx.CoordinateTransforms;
-
-
-/**
- * The forward transform function (that is, from the source projection to the
- * target projection) that takes a {@link ol.Coordinate} as argument
- * and returns the transformed {@link ol.Coordinate}.
- * @type {function(ol.Coordinate): ol.Coordinate}
- */
-olx.CoordinateTransforms.prototype.forward;
-
-
-/**
- * The inverse transform function (that is, from the target projection to the
- * source projection) that takes a {@link ol.Coordinate} as argument
- * and returns the transformed {@link ol.Coordinate}.
- * @type {function(ol.Coordinate): ol.Coordinate}
- */
-olx.CoordinateTransforms.prototype.inverse;
-
-
 /**
  * Object literal with config options for the projection.
  * @typedef {{code: string,
diff --git a/externs/proj4js.js b/externs/proj4js.js
index bcca8c150e..aca6cfd8e2 100644
--- a/externs/proj4js.js
+++ b/externs/proj4js.js
@@ -5,9 +5,12 @@
 
 
 /**
- * @type {Function}
+ * @param {...*} var_args
+ * @return {undefined|Array.<number>|Object.<{
+ *     forward: function(Array.<number>): Array.<number>,
+ *     inverse: function(Array.<number>): Array.<number>}>}
  */
-var proj4 = function() {};
+var proj4 = function(var_args) {};
 
 
 /**
diff --git a/src/ol/proj/proj.js b/src/ol/proj/proj.js
index 9578d350f3..62b3c585ec 100644
--- a/src/ol/proj/proj.js
+++ b/src/ol/proj/proj.js
@@ -385,25 +385,24 @@ ol.proj.addTransform = function(source, destination, transformFn) {
  *
  * @param {ol.proj.ProjectionLike} source Source projection.
  * @param {ol.proj.ProjectionLike} destination Destination projection.
- * @param {olx.CoordinateTransforms} transforms Forward and inverse transform
- *     functions.
+ * @param {function(ol.Coordinate): ol.Coordinate} forward The forward transform
+ *     function (that is, from the source projection to the destination
+ *     projection) that takes a {@link ol.Coordinate} as argument and returns
+ *     the transformed {@link ol.Coordinate}.
+ * @param {function(ol.Coordinate): ol.Coordinate} inverse The inverse transform
+ *     function (that is, from the destination projection to the source
+ *     projection) that takes a {@link ol.Coordinate} as argument and returns
+ *     the transformed {@link ol.Coordinate}.
  * @api
  */
-ol.proj.addCoordinateTransforms = function(source, destination, transforms) {
+ol.proj.addCoordinateTransforms =
+    function(source, destination, forward, inverse) {
   var sourceProj = ol.proj.get(source);
   var destProj = ol.proj.get(destination);
-  var forward, inverse;
-  if (sourceProj === destProj) {
-    forward = ol.proj.cloneTransform;
-    inverse = ol.proj.cloneTransform;
-  } else {
-    forward =
-        ol.proj.createTransformFromCoordinateTransform(transforms.forward);
-    inverse =
-        ol.proj.createTransformFromCoordinateTransform(transforms.inverse);
-  }
-  ol.proj.addTransform(sourceProj, destProj, forward);
-  ol.proj.addTransform(destProj, sourceProj, inverse);
+  ol.proj.addTransform(sourceProj, destProj,
+      ol.proj.createTransformFromCoordinateTransform(forward));
+  ol.proj.addTransform(destProj, sourceProj,
+      ol.proj.createTransformFromCoordinateTransform(inverse));
 };
 
 
@@ -494,7 +493,7 @@ ol.proj.get = function(projectionLike) {
           axisOrientation: def.axis
         });
         ol.proj.addProjection(projection);
-        var currentCode, currentDef, currentProj;
+        var currentCode, currentDef, currentProj, proj4Transform;
         for (currentCode in projections) {
           currentDef = proj4.defs(currentCode);
           if (goog.isDef(currentDef)) {
@@ -502,8 +501,9 @@ ol.proj.get = function(projectionLike) {
             if (currentDef === def) {
               ol.proj.addEquivalentProjections([currentProj, projection]);
             } else {
+              proj4Transform = proj4(currentCode, code);
               ol.proj.addCoordinateTransforms(currentProj, projection,
-                  proj4(currentCode, code));
+                  proj4Transform.forward, proj4Transform.inverse);
             }
           }
         }