diff --git a/src/ol/geom/geometry.js b/src/ol/geom/geometry.js
index 09d93cf5f2..0351bf22cd 100644
--- a/src/ol/geom/geometry.js
+++ b/src/ol/geom/geometry.js
@@ -3,9 +3,9 @@ goog.provide('ol.geom.GeometryEvent');
 goog.provide('ol.geom.GeometryType');
 
 goog.require('goog.events.Event');
-goog.require('goog.events.EventTarget');
 goog.require('goog.object');
 goog.require('ol.Extent');
+goog.require('ol.Observable');
 goog.require('ol.TransformFunction');
 
 
@@ -30,13 +30,13 @@ ol.geom.GeometryType = {
 
 /**
  * @constructor
- * @extends {goog.events.EventTarget}
+ * @extends {ol.Observable}
  * @todo stability experimental
  */
 ol.geom.Geometry = function() {
   goog.base(this);
 };
-goog.inherits(ol.geom.Geometry, goog.events.EventTarget);
+goog.inherits(ol.geom.Geometry, ol.Observable);
 
 
 /**
diff --git a/src/ol/interaction/drawinteraction.js b/src/ol/interaction/drawinteraction.js
index 6157a21131..b2bd009c99 100644
--- a/src/ol/interaction/drawinteraction.js
+++ b/src/ol/interaction/drawinteraction.js
@@ -10,6 +10,7 @@ goog.require('ol.MapBrowserEvent');
 goog.require('ol.MapBrowserEvent.EventType');
 goog.require('ol.geom.GeometryType');
 goog.require('ol.geom.LineString');
+goog.require('ol.geom.LinearRing');
 goog.require('ol.geom.MultiLineString');
 goog.require('ol.geom.MultiPoint');
 goog.require('ol.geom.MultiPolygon');
@@ -209,6 +210,7 @@ ol.interaction.Draw.prototype.atFinish_ = function(event) {
     if (this.mode_ === ol.interaction.DrawMode.LINESTRING) {
       potentiallyDone = geometry.getCoordinates().length > 2;
     } else if (this.mode_ === ol.interaction.DrawMode.POLYGON) {
+      goog.asserts.assertInstanceof(geometry, ol.geom.Polygon);
       potentiallyDone = geometry.getRings()[0].getCoordinates().length > 3;
     }
     if (potentiallyDone) {
@@ -270,22 +272,29 @@ ol.interaction.Draw.prototype.modifyDrawing_ = function(event) {
   var geometry = this.sketchFeature_.getGeometry();
   var coordinates, last;
   if (this.mode_ === ol.interaction.DrawMode.POINT) {
+    goog.asserts.assertInstanceof(geometry, ol.geom.Point);
     last = geometry.getCoordinates();
     last[0] = coordinate[0];
     last[1] = coordinate[1];
     geometry.setCoordinates(last);
   } else {
     if (this.mode_ === ol.interaction.DrawMode.LINESTRING) {
+      goog.asserts.assertInstanceof(geometry, ol.geom.LineString);
       coordinates = geometry.getCoordinates();
-    } else if (this.mode_ === ol.interaction.DrawMode.POLYGON) {
+    } else {
+      goog.asserts.assert(this.mode_ === ol.interaction.DrawMode.POLYGON);
+      goog.asserts.assertInstanceof(geometry, ol.geom.Polygon);
       geometry = geometry.getRings()[0];
+      goog.asserts.assertInstanceof(geometry, ol.geom.LinearRing);
       coordinates = geometry.getCoordinates();
     }
     if (this.atFinish_(event)) {
       // snap to finish
       coordinate = this.finishCoordinate_.slice();
     }
-    this.sketchPoint_.getGeometry().setCoordinates(coordinate);
+    var point = this.sketchPoint_.getGeometry();
+    goog.asserts.assertInstanceof(point, ol.geom.Point);
+    point.setCoordinates(coordinate);
     last = coordinates[coordinates.length - 1];
     last[0] = coordinate[0];
     last[1] = coordinate[1];
@@ -304,11 +313,13 @@ ol.interaction.Draw.prototype.addToDrawing_ = function(event) {
   var geometry = this.sketchFeature_.getGeometry();
   var coordinates, last;
   if (this.mode_ === ol.interaction.DrawMode.LINESTRING) {
+    goog.asserts.assertInstanceof(geometry, ol.geom.LineString);
     this.finishCoordinate_ = coordinate.slice();
     coordinates = geometry.getCoordinates();
     coordinates.push(coordinate.slice());
     geometry.setCoordinates(coordinates);
   } else if (this.mode_ === ol.interaction.DrawMode.POLYGON) {
+    goog.asserts.assertInstanceof(geometry, ol.geom.Polygon);
     var ring = geometry.getRings()[0];
     coordinates = ring.getCoordinates();
     coordinates.push(coordinate.slice());
@@ -329,10 +340,12 @@ ol.interaction.Draw.prototype.finishDrawing_ = function(event) {
   var geometry = sketchFeature.getGeometry();
   var coordinates = geometry.getCoordinates();
   if (this.mode_ === ol.interaction.DrawMode.LINESTRING) {
+    goog.asserts.assertInstanceof(geometry, ol.geom.LineString);
     // remove the redundant last point
     coordinates.pop();
     geometry.setCoordinates(coordinates);
   } else if (this.mode_ === ol.interaction.DrawMode.POLYGON) {
+    goog.asserts.assertInstanceof(geometry, ol.geom.Polygon);
     // force clockwise order for exterior ring
     sketchFeature.setGeometry(new ol.geom.Polygon(coordinates));
   }
diff --git a/src/ol/interaction/modifyinteraction.js b/src/ol/interaction/modifyinteraction.js
index 94fde65c71..33fc1fde76 100644
--- a/src/ol/interaction/modifyinteraction.js
+++ b/src/ol/interaction/modifyinteraction.js
@@ -339,8 +339,9 @@ ol.interaction.Modify.prototype.createOrUpdateVertexFeature_ =
     this.vertexFeature_ = vertexFeature;
     this.sketchLayer_.getVectorSource().addFeatures([vertexFeature]);
   } else {
-    var geometry = vertexFeature.getGeometry();
-    geometry.setCoordinates(coordinates);
+    var point = vertexFeature.getGeometry();
+    goog.asserts.assertInstanceof(point, ol.geom.Point);
+    point.setCoordinates(coordinates);
   }
   if (this.sketchLayer_.getStyle() !== style) {
     this.sketchLayer_.setStyle(style);
@@ -505,6 +506,7 @@ ol.interaction.Modify.prototype.insertVertex_ =
   var segment = segmentData.segment;
   var feature = segmentData.feature;
   var geometry = segmentData.geometry;
+  goog.asserts.assertInstanceof(geometry, ol.geom.LineString);
   var index = segmentData.index;
   var coordinates = geometry.getCoordinates();
   coordinates.splice(index + 1, 0, vertex);
diff --git a/src/ol/renderer/canvas/canvasvectorrenderer.js b/src/ol/renderer/canvas/canvasvectorrenderer.js
index 213f0e6cbc..c90bda9f7c 100644
--- a/src/ol/renderer/canvas/canvasvectorrenderer.js
+++ b/src/ol/renderer/canvas/canvasvectorrenderer.js
@@ -274,6 +274,7 @@ ol.renderer.canvas.Vector.prototype.renderPointFeatures_ =
     }
     for (j = 0, jj = components.length; j < jj; ++j) {
       point = components[j];
+      goog.asserts.assertInstanceof(point, ol.geom.Point);
       vec = [point.get(0), point.get(1), 0];
       goog.vec.Mat4.multVec3(this.transform_, vec, vec);
       context.drawImage(content, Math.round(vec[0] + xOffset),
@@ -406,6 +407,7 @@ ol.renderer.canvas.Vector.prototype.renderPolygonFeatures_ =
     }
     for (j = 0, jj = components.length; j < jj; ++j) {
       poly = components[j];
+      goog.asserts.assertInstanceof(poly, ol.geom.Polygon);
       rings = poly.getRings();
       numRings = rings.length;
       if (numRings > 0) {
@@ -537,9 +539,11 @@ ol.renderer.canvas.Vector.getLabelVectors = function(geometry) {
   }
   var type = geometry.getType();
   if (type == ol.geom.GeometryType.POINT) {
+    goog.asserts.assertInstanceof(geometry, ol.geom.Point);
     return [[geometry.get(0), geometry.get(1), 0]];
   }
   if (type == ol.geom.GeometryType.POLYGON) {
+    goog.asserts.assertInstanceof(geometry, ol.geom.Polygon);
     var coordinates = geometry.getInteriorPoint();
     return [[coordinates[0], coordinates[1], 0]];
   }
diff --git a/test/spec/ol/geom/geometry.test.js b/test/spec/ol/geom/geometry.test.js
index a2898d1fe8..25949ffb84 100644
--- a/test/spec/ol/geom/geometry.test.js
+++ b/test/spec/ol/geom/geometry.test.js
@@ -6,7 +6,7 @@ describe('ol.geom.Geometry', function() {
     it('creates a new geometry', function() {
       var geom = new ol.geom.Geometry();
       expect(geom).to.be.a(ol.geom.Geometry);
-      expect(geom).to.be.a(goog.events.EventTarget);
+      expect(geom).to.be.a(ol.Observable);
     });
   });
 
@@ -45,7 +45,7 @@ describe('ol.geom.GeometryEvent', function() {
 });
 
 goog.require('goog.events.Event');
-goog.require('goog.events.EventTarget');
+goog.require('ol.Observable');
 goog.require('ol.geom.Geometry');
 goog.require('ol.geom.GeometryEvent');
 goog.require('ol.geom.Point');