diff --git a/src/ol/geolocation.js b/src/ol/geolocation.js
index c218792596..c6d35470d8 100644
--- a/src/ol/geolocation.js
+++ b/src/ol/geolocation.js
@@ -134,7 +134,7 @@ ol.Geolocation.prototype.handleProjectionChanged_ = function() {
 ol.Geolocation.prototype.handleTrackingChanged_ = function() {
   if (ol.has.GEOLOCATION) {
     var tracking = this.getTracking();
-    if (tracking && !goog.isDef(this.watchId_)) {
+    if (tracking && this.watchId_ === undefined) {
       this.watchId_ = goog.global.navigator.geolocation.watchPosition(
           goog.bind(this.positionChange_, this),
           goog.bind(this.positionError_, this),
diff --git a/src/ol/map.js b/src/ol/map.js
index acb08063c9..cf7e509e68 100644
--- a/src/ol/map.js
+++ b/src/ol/map.js
@@ -1466,7 +1466,7 @@ ol.Map.createOptionsInternal = function(options) {
   var values = {};
 
   var logos = {};
-  if (!goog.isDef(options.logo) ||
+  if (options.logo === undefined ||
       (goog.isBoolean(options.logo) && options.logo)) {
     logos[ol.OL3_LOGO_URL] = ol.OL3_URL;
   } else {
diff --git a/src/ol/proj/proj.js b/src/ol/proj/proj.js
index a909eba5c0..dd14c7fded 100644
--- a/src/ol/proj/proj.js
+++ b/src/ol/proj/proj.js
@@ -149,7 +149,7 @@ ol.proj.Projection = function(options) {
       !goog.isDef(projections[code])) {
     var def = proj4.defs(code);
     if (def !== undefined) {
-      if (goog.isDef(def.axis) && !goog.isDef(options.axisOrientation)) {
+      if (goog.isDef(def.axis) && options.axisOrientation === undefined) {
         this.axisOrientation_ = def.axis;
       }
       if (options.units === undefined) {
diff --git a/src/ol/renderer/webgl/webgllayerrenderer.js b/src/ol/renderer/webgl/webgllayerrenderer.js
index 1a152affec..9363754aac 100644
--- a/src/ol/renderer/webgl/webgllayerrenderer.js
+++ b/src/ol/renderer/webgl/webgllayerrenderer.js
@@ -110,7 +110,7 @@ ol.renderer.webgl.Layer.prototype.bindFramebuffer =
 
   var gl = this.mapRenderer.getGL();
 
-  if (!goog.isDef(this.framebufferDimension) ||
+  if (this.framebufferDimension === undefined ||
       this.framebufferDimension != framebufferDimension) {
 
     frameState.postRenderFunctions.push(
diff --git a/src/ol/source/imagewmssource.js b/src/ol/source/imagewmssource.js
index 06e36fcb85..4f99ac2a82 100644
--- a/src/ol/source/imagewmssource.js
+++ b/src/ol/source/imagewmssource.js
@@ -194,7 +194,7 @@ ol.source.ImageWMS.prototype.getImage =
 
   resolution = this.findNearestResolution(resolution);
 
-  if (pixelRatio != 1 && (!this.hidpi_ || !goog.isDef(this.serverType_))) {
+  if (pixelRatio != 1 && (!this.hidpi_ || this.serverType_ === undefined)) {
     pixelRatio = 1;
   }
 
diff --git a/src/ol/source/tilewmssource.js b/src/ol/source/tilewmssource.js
index 4d1ae44934..09c7f6e504 100644
--- a/src/ol/source/tilewmssource.js
+++ b/src/ol/source/tilewmssource.js
@@ -292,7 +292,7 @@ ol.source.TileWMS.prototype.getRequestUrl_ =
 ol.source.TileWMS.prototype.getTilePixelSize =
     function(z, pixelRatio, projection) {
   var tileSize = goog.base(this, 'getTilePixelSize', z, pixelRatio, projection);
-  if (pixelRatio == 1 || !this.hidpi_ || !goog.isDef(this.serverType_)) {
+  if (pixelRatio == 1 || !this.hidpi_ || this.serverType_ === undefined) {
     return tileSize;
   } else {
     return ol.size.scale(tileSize, pixelRatio, this.tmpSize);
@@ -373,7 +373,7 @@ ol.source.TileWMS.prototype.tileUrlFunction_ =
     return undefined;
   }
 
-  if (pixelRatio != 1 && (!this.hidpi_ || !goog.isDef(this.serverType_))) {
+  if (pixelRatio != 1 && (!this.hidpi_ || this.serverType_ === undefined)) {
     pixelRatio = 1;
   }