diff --git a/src/ol/geom/flat/flipflatgeom.js b/src/ol/geom/flat/flipflatgeom.js
index fbf6bd7c72..8532682e46 100644
--- a/src/ol/geom/flat/flipflatgeom.js
+++ b/src/ol/geom/flat/flipflatgeom.js
@@ -19,7 +19,7 @@ ol.geom.flat.flip.flipXY =
     dest = opt_dest;
     destOffset = goog.isDef(opt_destOffset) ? opt_destOffset : 0;
   } else {
-    goog.asserts.assert(!goog.isDef(opt_destOffset),
+    goog.asserts.assert(opt_destOffset === undefined,
         'opt_destOffSet should be defined');
     dest = [];
     destOffset = 0;
diff --git a/src/ol/overlay.js b/src/ol/overlay.js
index c9bda6cb0b..71b3f649d8 100644
--- a/src/ol/overlay.js
+++ b/src/ol/overlay.js
@@ -366,7 +366,7 @@ ol.Overlay.prototype.panIntoView_ = function() {
   goog.asserts.assert(this.autoPan, 'this.autoPan should be true');
   var map = this.getMap();
 
-  if (!goog.isDef(map) || goog.isNull(map.getTargetElement())) {
+  if (map === undefined || goog.isNull(map.getTargetElement())) {
     return;
   }
 
@@ -474,7 +474,7 @@ ol.Overlay.prototype.setVisible = function(visible) {
 ol.Overlay.prototype.updatePixelPosition = function() {
   var map = this.getMap();
   var position = this.getPosition();
-  if (!goog.isDef(map) || !map.isRendered() || !goog.isDef(position)) {
+  if (map === undefined || !map.isRendered() || position === undefined) {
     this.setVisible(false);
     return;
   }
diff --git a/src/ol/proj/proj.js b/src/ol/proj/proj.js
index 821b133e8d..27d0f42873 100644
--- a/src/ol/proj/proj.js
+++ b/src/ol/proj/proj.js
@@ -652,7 +652,7 @@ ol.proj.get = function(projectionLike) {
   } else if (goog.isString(projectionLike)) {
     var code = projectionLike;
     projection = ol.proj.projections_[code];
-    if (ol.ENABLE_PROJ4JS && !goog.isDef(projection) &&
+    if (ol.ENABLE_PROJ4JS && projection === undefined &&
         typeof proj4 == 'function' && goog.isDef(proj4.defs(code))) {
       projection = new ol.proj.Projection({code: code});
       ol.proj.addProjection(projection);
diff --git a/src/ol/render/canvas/canvasreplay.js b/src/ol/render/canvas/canvasreplay.js
index 96a96951cb..8de2dbecb3 100644
--- a/src/ol/render/canvas/canvasreplay.js
+++ b/src/ol/render/canvas/canvasreplay.js
@@ -1007,7 +1007,7 @@ ol.render.canvas.LineStringReplay.prototype.drawLineStringGeometry =
   goog.asserts.assert(!goog.isNull(state), 'state should not be null');
   var strokeStyle = state.strokeStyle;
   var lineWidth = state.lineWidth;
-  if (!goog.isDef(strokeStyle) || !goog.isDef(lineWidth)) {
+  if (strokeStyle === undefined || lineWidth === undefined) {
     return;
   }
   this.setStrokeStyle_();
@@ -1035,7 +1035,7 @@ ol.render.canvas.LineStringReplay.prototype.drawMultiLineStringGeometry =
   goog.asserts.assert(!goog.isNull(state), 'state should not be null');
   var strokeStyle = state.strokeStyle;
   var lineWidth = state.lineWidth;
-  if (!goog.isDef(strokeStyle) || !goog.isDef(lineWidth)) {
+  if (strokeStyle === undefined || lineWidth === undefined) {
     return;
   }
   this.setStrokeStyle_();
@@ -1217,7 +1217,7 @@ ol.render.canvas.PolygonReplay.prototype.drawCircleGeometry =
   goog.asserts.assert(!goog.isNull(state), 'state should not be null');
   var fillStyle = state.fillStyle;
   var strokeStyle = state.strokeStyle;
-  if (!goog.isDef(fillStyle) && !goog.isDef(strokeStyle)) {
+  if (fillStyle === undefined && strokeStyle === undefined) {
     return;
   }
   if (strokeStyle !== undefined) {
@@ -1270,7 +1270,7 @@ ol.render.canvas.PolygonReplay.prototype.drawPolygonGeometry =
   goog.asserts.assert(!goog.isNull(state), 'state should not be null');
   var fillStyle = state.fillStyle;
   var strokeStyle = state.strokeStyle;
-  if (!goog.isDef(fillStyle) && !goog.isDef(strokeStyle)) {
+  if (fillStyle === undefined && strokeStyle === undefined) {
     return;
   }
   if (strokeStyle !== undefined) {
@@ -1306,7 +1306,7 @@ ol.render.canvas.PolygonReplay.prototype.drawMultiPolygonGeometry =
   goog.asserts.assert(!goog.isNull(state), 'state should not be null');
   var fillStyle = state.fillStyle;
   var strokeStyle = state.strokeStyle;
-  if (!goog.isDef(fillStyle) && !goog.isDef(strokeStyle)) {
+  if (fillStyle === undefined && strokeStyle === undefined) {
     return;
   }
   if (strokeStyle !== undefined) {
diff --git a/src/ol/render/webgl/webglreplay.js b/src/ol/render/webgl/webglreplay.js
index 122cafb759..9508c34470 100644
--- a/src/ol/render/webgl/webglreplay.js
+++ b/src/ol/render/webgl/webglreplay.js
@@ -866,7 +866,7 @@ ol.render.webgl.ImageReplay.prototype.drawHitDetectionReplayOneByOne_ =
 
       if (!goog.isDef(skippedFeaturesHash[featureUid]) &&
           goog.isDefAndNotNull(feature.getGeometry()) &&
-          (!goog.isDef(opt_hitExtent) || ol.extent.intersects(
+          (opt_hitExtent === undefined || ol.extent.intersects(
               opt_hitExtent, feature.getGeometry().getExtent()))) {
         gl.clear(gl.COLOR_BUFFER_BIT | gl.DEPTH_BUFFER_BIT);
         this.drawElements_(gl, start, end, elementType, elementSize);
diff --git a/src/ol/source/tilearcgisrestsource.js b/src/ol/source/tilearcgisrestsource.js
index 8ec3c9e74c..e1093f1006 100644
--- a/src/ol/source/tilearcgisrestsource.js
+++ b/src/ol/source/tilearcgisrestsource.js
@@ -48,7 +48,7 @@ ol.source.TileArcGISRest = function(opt_options) {
   });
 
   var urls = options.urls;
-  if (!goog.isDef(urls) && goog.isDef(options.url)) {
+  if (urls === undefined && goog.isDef(options.url)) {
     urls = ol.TileUrlFunction.expandUrl(options.url);
   }
 
diff --git a/src/ol/source/tilewmssource.js b/src/ol/source/tilewmssource.js
index 8a17db97da..12f8eff1d3 100644
--- a/src/ol/source/tilewmssource.js
+++ b/src/ol/source/tilewmssource.js
@@ -52,7 +52,7 @@ ol.source.TileWMS = function(opt_options) {
   });
 
   var urls = options.urls;
-  if (!goog.isDef(urls) && goog.isDef(options.url)) {
+  if (urls === undefined && goog.isDef(options.url)) {
     urls = ol.TileUrlFunction.expandUrl(options.url);
   }
 
diff --git a/src/ol/source/vectorsource.js b/src/ol/source/vectorsource.js
index 074154a968..bf698e6ea0 100644
--- a/src/ol/source/vectorsource.js
+++ b/src/ol/source/vectorsource.js
@@ -161,7 +161,7 @@ ol.source.Vector = function(opt_options) {
   } else if (goog.isArray(options.features)) {
     features = options.features;
   }
-  if (!useSpatialIndex && !goog.isDef(collection)) {
+  if (!useSpatialIndex && collection === undefined) {
     collection = new ol.Collection(features);
   }
   if (features !== undefined) {
diff --git a/src/ol/source/wmtssource.js b/src/ol/source/wmtssource.js
index 616c82d843..698a003576 100644
--- a/src/ol/source/wmtssource.js
+++ b/src/ol/source/wmtssource.js
@@ -83,7 +83,7 @@ ol.source.WMTS = function(options) {
   this.style_ = options.style;
 
   var urls = options.urls;
-  if (!goog.isDef(urls) && goog.isDef(options.url)) {
+  if (urls === undefined && goog.isDef(options.url)) {
     urls = ol.TileUrlFunction.expandUrl(options.url);
   }
 
diff --git a/src/ol/style/iconstyle.js b/src/ol/style/iconstyle.js
index 87d13574a2..edbb76b90c 100644
--- a/src/ol/style/iconstyle.js
+++ b/src/ol/style/iconstyle.js
@@ -108,13 +108,13 @@ ol.style.Icon = function(opt_options) {
   goog.asserts.assert(!(goog.isDef(src) && !goog.isNull(image)),
       'image and src can not provided at the same time');
   goog.asserts.assert(
-      !goog.isDef(src) || (goog.isDef(src) && goog.isNull(imgSize)),
+      src === undefined || (goog.isDef(src) && goog.isNull(imgSize)),
       'imgSize should not be set when src is provided');
   goog.asserts.assert(
       goog.isNull(image) || (!goog.isNull(image) && !goog.isNull(imgSize)),
       'imgSize must be set when image is provided');
 
-  if ((!goog.isDef(src) || src.length === 0) && !goog.isNull(image)) {
+  if ((src === undefined || src.length === 0) && !goog.isNull(image)) {
     src = image.src;
   }
   goog.asserts.assert(goog.isDef(src) && src.length > 0,
diff --git a/src/ol/view.js b/src/ol/view.js
index fb2092c2b7..059d0da86a 100644
--- a/src/ol/view.js
+++ b/src/ol/view.js
@@ -738,7 +738,7 @@ ol.View.createRotationConstraint_ = function(options) {
       options.enableRotation : true;
   if (enableRotation) {
     var constrainRotation = options.constrainRotation;
-    if (!goog.isDef(constrainRotation) || constrainRotation === true) {
+    if (constrainRotation === undefined || constrainRotation === true) {
       return ol.RotationConstraint.createSnapToZero();
     } else if (constrainRotation === false) {
       return ol.RotationConstraint.none;