diff --git a/src/ol/overlay.js b/src/ol/overlay.js
index 33c12c7cf9..9b2a103c4b 100644
--- a/src/ol/overlay.js
+++ b/src/ol/overlay.js
@@ -297,7 +297,7 @@ ol.Overlay.prototype.handleOffsetChanged = function() {
  */
 ol.Overlay.prototype.handlePositionChanged = function() {
   this.updatePixelPosition();
-  if (goog.isDef(this.get(ol.OverlayProperty.POSITION)) && this.autoPan) {
+  if (this.get(ol.OverlayProperty.POSITION) !== undefined && this.autoPan) {
     this.panIntoView_();
   }
 };
diff --git a/src/ol/proj/proj.js b/src/ol/proj/proj.js
index b79aadfefb..260b72d2aa 100644
--- a/src/ol/proj/proj.js
+++ b/src/ol/proj/proj.js
@@ -653,7 +653,7 @@ ol.proj.get = function(projectionLike) {
     var code = projectionLike;
     projection = ol.proj.projections_[code];
     if (ol.ENABLE_PROJ4JS && projection === undefined &&
-        typeof proj4 == 'function' && goog.isDef(proj4.defs(code))) {
+        typeof proj4 == 'function' && proj4.defs(code) !== undefined) {
       projection = new ol.proj.Projection({code: code});
       ol.proj.addProjection(projection);
     }
diff --git a/src/ol/renderer/canvas/canvasvectorlayerrenderer.js b/src/ol/renderer/canvas/canvasvectorlayerrenderer.js
index 6c55c66bbd..669937ec61 100644
--- a/src/ol/renderer/canvas/canvasvectorlayerrenderer.js
+++ b/src/ol/renderer/canvas/canvasvectorlayerrenderer.js
@@ -275,10 +275,14 @@ ol.renderer.canvas.VectorLayer.prototype.prepareFrame =
        */
       function(feature) {
     var styles;
-    if (goog.isDef(feature.getStyleFunction())) {
-      styles = feature.getStyleFunction().call(feature, resolution);
-    } else if (goog.isDef(vectorLayer.getStyleFunction())) {
-      styles = vectorLayer.getStyleFunction()(feature, resolution);
+    var styleFunction = feature.getStyleFunction();
+    if (styleFunction) {
+      styles = styleFunction.call(feature, resolution);
+    } else {
+      styleFunction = vectorLayer.getStyleFunction();
+      if (styleFunction) {
+        styles = styleFunction(feature, resolution);
+      }
     }
     if (goog.isDefAndNotNull(styles)) {
       var dirty = this.renderFeature(
diff --git a/src/ol/renderer/dom/domvectorlayerrenderer.js b/src/ol/renderer/dom/domvectorlayerrenderer.js
index 65603d5586..0cda31c2a3 100644
--- a/src/ol/renderer/dom/domvectorlayerrenderer.js
+++ b/src/ol/renderer/dom/domvectorlayerrenderer.js
@@ -283,10 +283,14 @@ ol.renderer.dom.VectorLayer.prototype.prepareFrame =
        */
       function(feature) {
     var styles;
-    if (goog.isDef(feature.getStyleFunction())) {
-      styles = feature.getStyleFunction().call(feature, resolution);
-    } else if (goog.isDef(vectorLayer.getStyleFunction())) {
-      styles = vectorLayer.getStyleFunction()(feature, resolution);
+    var styleFunction = feature.getStyleFunction();
+    if (styleFunction) {
+      styles = styleFunction.call(feature, resolution);
+    } else {
+      styleFunction = vectorLayer.getStyleFunction();
+      if (styleFunction) {
+        styles = styleFunction(feature, resolution);
+      }
     }
     if (goog.isDefAndNotNull(styles)) {
       var dirty = this.renderFeature(
diff --git a/src/ol/renderer/webgl/webglvectorlayerrenderer.js b/src/ol/renderer/webgl/webglvectorlayerrenderer.js
index 4d5a28f72b..551d4caeff 100644
--- a/src/ol/renderer/webgl/webglvectorlayerrenderer.js
+++ b/src/ol/renderer/webgl/webglvectorlayerrenderer.js
@@ -256,10 +256,14 @@ ol.renderer.webgl.VectorLayer.prototype.prepareFrame =
        */
       function(feature) {
     var styles;
-    if (goog.isDef(feature.getStyleFunction())) {
-      styles = feature.getStyleFunction().call(feature, resolution);
-    } else if (goog.isDef(vectorLayer.getStyleFunction())) {
-      styles = vectorLayer.getStyleFunction()(feature, resolution);
+    var styleFunction = feature.getStyleFunction();
+    if (styleFunction) {
+      styles = styleFunction.call(feature, resolution);
+    } else {
+      styleFunction = vectorLayer.getStyleFunction();
+      if (styleFunction) {
+        styles = styleFunction(feature, resolution);
+      }
     }
     if (goog.isDefAndNotNull(styles)) {
       var dirty = this.renderFeature(
diff --git a/src/ol/source/imagevectorsource.js b/src/ol/source/imagevectorsource.js
index f1dd179192..86594e4188 100644
--- a/src/ol/source/imagevectorsource.js
+++ b/src/ol/source/imagevectorsource.js
@@ -259,9 +259,10 @@ ol.source.ImageVector.prototype.handleSourceChange_ = function() {
 ol.source.ImageVector.prototype.renderFeature_ =
     function(feature, resolution, pixelRatio, replayGroup) {
   var styles;
-  if (goog.isDef(feature.getStyleFunction())) {
-    styles = feature.getStyleFunction().call(feature, resolution);
-  } else if (this.styleFunction_ !== undefined) {
+  var styleFunction = feature.getStyleFunction();
+  if (styleFunction) {
+    styles = styleFunction.call(feature, resolution);
+  } else if (this.styleFunction_) {
     styles = this.styleFunction_(feature, resolution);
   }
   if (!goog.isDefAndNotNull(styles)) {
diff --git a/src/ol/view.js b/src/ol/view.js
index 137fa94dd0..e06c0e670c 100644
--- a/src/ol/view.js
+++ b/src/ol/view.js
@@ -553,7 +553,7 @@ ol.View.prototype.centerOn = function(coordinate, size, position) {
  */
 ol.View.prototype.isDef = function() {
   return goog.isDefAndNotNull(this.getCenter()) &&
-      goog.isDef(this.getResolution());
+      this.getResolution() !== undefined;
 };