diff --git a/src/ol/proj/proj.js b/src/ol/proj/proj.js
index d6fa643b4f..a82f443bbf 100644
--- a/src/ol/proj/proj.js
+++ b/src/ol/proj/proj.js
@@ -139,19 +139,12 @@ ol.Projection.prototype.getUnits = function() {
 
 
 /**
- * Get the amount of meters per unit of this projection.
- * @return {number} Meters.
+ * Get the amount of meters per unit of this projection.  If the projection is
+ * not configured with a units identifier, the return is `undefined`.
+ * @return {number|undefined} Meters.
  */
 ol.Projection.prototype.getMetersPerUnit = function() {
-  var metersPerUnit;
-  if (!goog.isNull(this.units_)) {
-    metersPerUnit = ol.METERS_PER_UNIT[this.units_];
-  } else {
-    if (this instanceof ol.Proj4jsProjection_) {
-      metersPerUnit = this.getProj4jsProj().to_meter;
-    }
-  }
-  return metersPerUnit;
+  return ol.METERS_PER_UNIT[this.units_];
 };
 
 
@@ -231,6 +224,18 @@ ol.Proj4jsProjection_ = function(proj4jsProj, options) {
 goog.inherits(ol.Proj4jsProjection_, ol.Projection);
 
 
+/**
+ * @inheritDoc
+ */
+ol.Proj4jsProjection_.prototype.getMetersPerUnit = function() {
+  var metersPerUnit = this.proj4jsProj_.to_meter;
+  if (!goog.isDef(metersPerUnit)) {
+    metersPerUnit = ol.METERS_PER_UNIT[this.units_];
+  }
+  return metersPerUnit;
+};
+
+
 /**
  * @inheritDoc
  */