diff --git a/src/objectliterals.exports b/src/objectliterals.exports
index f94f2d9076..dd1ae0d5f8 100644
--- a/src/objectliterals.exports
+++ b/src/objectliterals.exports
@@ -11,7 +11,7 @@
 @exportObjectLiteralProperty ol.View2DOptions.center ol.Coordinate|undefined
 @exportObjectLiteralProperty ol.View2DOptions.maxResolution number|undefined
 @exportObjectLiteralProperty ol.View2DOptions.numZoomLevels number|undefined
-@exportObjectLiteralProperty ol.View2DOptions.projection ol.Projection|string|undefined
+@exportObjectLiteralProperty ol.View2DOptions.projection ol.ProjectionLike
 @exportObjectLiteralProperty ol.View2DOptions.resolution number|undefined
 @exportObjectLiteralProperty ol.View2DOptions.resolutions Array.<number>|undefined
 @exportObjectLiteralProperty ol.View2DOptions.rotation number|undefined
@@ -61,7 +61,7 @@
 @exportObjectLiteral ol.control.MousePositionOptions
 @exportObjectLiteralProperty ol.control.MousePositionOptions.coordinateFormat ol.CoordinateFormatType|undefined
 @exportObjectLiteralProperty ol.control.MousePositionOptions.map ol.Map|undefined
-@exportObjectLiteralProperty ol.control.MousePositionOptions.projection ol.Projection|undefined
+@exportObjectLiteralProperty ol.control.MousePositionOptions.projection ol.ProjectionLike
 @exportObjectLiteralProperty ol.control.MousePositionOptions.target Element|undefined
 @exportObjectLiteralProperty ol.control.MousePositionOptions.undefinedHTML string|undefined
 
@@ -103,7 +103,7 @@
 
 @exportObjectLiteral ol.source.DebugTileSourceOptions
 @exportObjectLiteralProperty ol.source.DebugTileSourceOptions.extent ol.Extent|undefined
-@exportObjectLiteralProperty ol.source.DebugTileSourceOptions.projection ol.Projection|undefined
+@exportObjectLiteralProperty ol.source.DebugTileSourceOptions.projection ol.ProjectionLike
 @exportObjectLiteralProperty ol.source.DebugTileSourceOptions.tileGrid ol.tilegrid.TileGrid|undefined
 
 @exportObjectLiteral ol.source.SingleImageWMSOptions
@@ -111,7 +111,7 @@
 @exportObjectLiteralProperty ol.source.SingleImageWMSOptions.crossOrigin null|string|undefined
 @exportObjectLiteralProperty ol.source.SingleImageWMSOptions.extent ol.Extent|undefined
 @exportObjectLiteralProperty ol.source.SingleImageWMSOptions.params Object.<string,*>
-@exportObjectLiteralProperty ol.source.SingleImageWMSOptions.projection ol.Projection|undefined
+@exportObjectLiteralProperty ol.source.SingleImageWMSOptions.projection ol.ProjectionLike
 @exportObjectLiteralProperty ol.source.SingleImageWMSOptions.resolutions Array.<number>|undefined
 @exportObjectLiteralProperty ol.source.SingleImageWMSOptions.url string|undefined
 
@@ -128,7 +128,7 @@
 @exportObjectLiteralProperty ol.source.StaticImageOptions.extent ol.Extent|undefined
 @exportObjectLiteralProperty ol.source.StaticImageOptions.imageExtent ol.Extent|undefined
 @exportObjectLiteralProperty ol.source.StaticImageOptions.imageSize ol.Size|undefined
-@exportObjectLiteralProperty ol.source.StaticImageOptions.projection ol.Projection|undefined
+@exportObjectLiteralProperty ol.source.StaticImageOptions.projection ol.ProjectionLike
 @exportObjectLiteralProperty ol.source.StaticImageOptions.url string|undefined
 
 @exportObjectLiteral ol.source.TiledWMSOptions
@@ -138,7 +138,7 @@
 @exportObjectLiteralProperty ol.source.TiledWMSOptions.extent ol.Extent|undefined
 @exportObjectLiteralProperty ol.source.TiledWMSOptions.tileGrid ol.tilegrid.TileGrid|undefined
 @exportObjectLiteralProperty ol.source.TiledWMSOptions.maxZoom number|undefined
-@exportObjectLiteralProperty ol.source.TiledWMSOptions.projection ol.Projection|undefined
+@exportObjectLiteralProperty ol.source.TiledWMSOptions.projection ol.ProjectionLike
 @exportObjectLiteralProperty ol.source.TiledWMSOptions.url string|undefined
 @exportObjectLiteralProperty ol.source.TiledWMSOptions.urls Array.<string>|undefined
 
diff --git a/src/ol/control/mousepositioncontrol.js b/src/ol/control/mousepositioncontrol.js
index fc736fe5a2..aa0b1f39a9 100644
--- a/src/ol/control/mousepositioncontrol.js
+++ b/src/ol/control/mousepositioncontrol.js
@@ -41,9 +41,9 @@ ol.control.MousePosition = function(opt_options) {
 
   /**
    * @private
-   * @type {ol.Projection|undefined}
+   * @type {ol.Projection}
    */
-  this.projection_ = options.projection;
+  this.projection_ = ol.projection.get(options.projection);
 
   /**
    * @private
@@ -168,7 +168,7 @@ ol.control.MousePosition.prototype.updateHTML_ = function(pixel) {
   var html = this.undefinedHTML_;
   if (!goog.isNull(pixel)) {
     if (this.renderedProjection_ != this.mapProjection_) {
-      if (goog.isDef(this.projection_)) {
+      if (!goog.isNull(this.projection_)) {
         this.transform_ = ol.projection.getTransform(
             this.mapProjection_, this.projection_);
       } else {
diff --git a/src/ol/projection.js b/src/ol/projection.js
index 512444c766..e3d5e22ee2 100644
--- a/src/ol/projection.js
+++ b/src/ol/projection.js
@@ -1,4 +1,5 @@
 goog.provide('ol.Projection');
+goog.provide('ol.ProjectionLike');
 goog.provide('ol.ProjectionUnits');
 goog.provide('ol.projection');
 
@@ -23,6 +24,12 @@ ol.ENABLE_PROJ4JS = true;
 ol.HAVE_PROJ4JS = ol.ENABLE_PROJ4JS && typeof Proj4js == 'object';
 
 
+/**
+ * @typedef {ol.Projection|string|undefined}
+ */
+ol.ProjectionLike;
+
+
 /**
  * @enum {string}
  */
@@ -422,20 +429,29 @@ ol.projection.removeTransform = function(source, destination) {
 
 
 /**
- * @param {string} code Code which is a combination of authority and identifier
- *   such as “EPSG:4326”.
+ * @param {ol.ProjectionLike} projectionLike Either a code string which is a
+ *     combination of authority and identifier such as “EPSG:4326”, or an
+ *     existing projection object, or undefined.
  * @return {ol.Projection} Projection.
  */
-ol.projection.get = function(code) {
-  var projection = ol.projection.projections_[code];
-  if (ol.HAVE_PROJ4JS && !goog.isDef(projection)) {
-    projection = ol.projection.getProj4jsProjectionFromCode_({
-      code: code,
-      extent: null
-    });
-  }
-  if (!goog.isDef(projection)) {
-    goog.asserts.assert(goog.isDef(projection));
+ol.projection.get = function(projectionLike) {
+  var projection;
+  if (projectionLike instanceof ol.Projection) {
+    projection = projectionLike;
+  } else if (goog.isString(projectionLike)) {
+    var code = projectionLike;
+    projection = ol.projection.projections_[code];
+    if (ol.HAVE_PROJ4JS && !goog.isDef(projection)) {
+      projection = ol.projection.getProj4jsProjectionFromCode_({
+        code: code,
+        extent: null
+      });
+    }
+    if (!goog.isDef(projection)) {
+      goog.asserts.assert(goog.isDef(projection));
+      projection = null;
+    }
+  } else {
     projection = null;
   }
   return projection;
diff --git a/src/ol/source/imagesource.js b/src/ol/source/imagesource.js
index 70c980afb2..b96973af8b 100644
--- a/src/ol/source/imagesource.js
+++ b/src/ol/source/imagesource.js
@@ -16,7 +16,7 @@ goog.require('ol.source.Source');
  * @typedef {{attributions: (Array.<ol.Attribution>|undefined),
  *            crossOrigin: (null|string|undefined),
  *            extent: (null|ol.Extent|undefined),
- *            projection: (ol.Projection|undefined),
+ *            projection: ol.ProjectionLike,
  *            resolutions: (Array.<number>|undefined),
  *            imageUrlFunction: (ol.ImageUrlFunctionType|
  *                undefined)}}
diff --git a/src/ol/source/imagetilesource.js b/src/ol/source/imagetilesource.js
index b9fd30f9ea..646c5ec18a 100644
--- a/src/ol/source/imagetilesource.js
+++ b/src/ol/source/imagetilesource.js
@@ -18,7 +18,7 @@ goog.require('ol.tilegrid.TileGrid');
  *            crossOrigin: (null|string|undefined),
  *            extent: (ol.Extent|undefined),
  *            opaque: (boolean|undefined),
- *            projection: (ol.Projection|undefined),
+ *            projection: ol.ProjectionLike,
  *            tileGrid: (ol.tilegrid.TileGrid|undefined),
  *            tileUrlFunction: (ol.TileUrlFunctionType|undefined)}}
  */
diff --git a/src/ol/source/source.js b/src/ol/source/source.js
index 2bc657b57c..8245f26e69 100644
--- a/src/ol/source/source.js
+++ b/src/ol/source/source.js
@@ -5,13 +5,13 @@ goog.require('goog.events.EventType');
 goog.require('goog.functions');
 goog.require('ol.Attribution');
 goog.require('ol.Extent');
-goog.require('ol.Projection');
+goog.require('ol.projection');
 
 
 /**
  * @typedef {{attributions: (Array.<ol.Attribution>|undefined),
  *            extent: (ol.Extent|undefined),
- *            projection: (ol.Projection|undefined)}}
+ *            projection: ol.ProjectionLike}}
  */
 ol.source.SourceOptions;
 
@@ -30,8 +30,7 @@ ol.source.Source = function(sourceOptions) {
    * @private
    * @type {ol.Projection}
    */
-  this.projection_ = goog.isDef(sourceOptions.projection) ?
-      sourceOptions.projection : null;
+  this.projection_ = ol.projection.get(sourceOptions.projection);
 
   /**
    * @private
diff --git a/src/ol/source/staticimagesource.js b/src/ol/source/staticimagesource.js
index b1d15bcbe0..d788e20fa5 100644
--- a/src/ol/source/staticimagesource.js
+++ b/src/ol/source/staticimagesource.js
@@ -2,6 +2,7 @@ goog.provide('ol.source.StaticImage');
 
 goog.require('ol.Image');
 goog.require('ol.ImageUrlFunctionType');
+goog.require('ol.projection');
 goog.require('ol.source.ImageSource');
 
 
@@ -19,7 +20,7 @@ ol.source.StaticImage = function(options) {
   var imageExtent = options.imageExtent;
   var imageSize = options.imageSize;
   var imageResolution = imageExtent.getHeight() / imageSize.height;
-  var projection = goog.isDef(options.projection) ? options.projection : null;
+  var projection = ol.projection.get(options.projection);
 
   goog.base(this, {
     attributions: options.attributions,
diff --git a/src/ol/source/tilesource.js b/src/ol/source/tilesource.js
index 92bd61caf3..9244a53e7b 100644
--- a/src/ol/source/tilesource.js
+++ b/src/ol/source/tilesource.js
@@ -4,7 +4,6 @@ goog.provide('ol.source.TileSourceOptions');
 goog.require('goog.functions');
 goog.require('ol.Attribution');
 goog.require('ol.Extent');
-goog.require('ol.Projection');
 goog.require('ol.Tile');
 goog.require('ol.TileCoord');
 goog.require('ol.TileRange');
@@ -16,7 +15,7 @@ goog.require('ol.tilegrid.TileGrid');
  * @typedef {{attributions: (Array.<ol.Attribution>|undefined),
  *            extent: (ol.Extent|undefined),
  *            opaque: (boolean|undefined),
- *            projection: (ol.Projection|undefined),
+ *            projection: ol.ProjectionLike,
  *            tileGrid: (ol.tilegrid.TileGrid|undefined)}}
  */
 ol.source.TileSourceOptions;