diff --git a/web/compatibility.js b/web/compatibility.js
index 26405ad8f..b22153516 100644
--- a/web/compatibility.js
+++ b/web/compatibility.js
@@ -224,3 +224,10 @@
     }
   });
 })();
+
+// Check console compatability
+(function checkConsoleCompatibility() {
+  if (typeof console == 'undefined') {
+    console = {log: function() {}};
+  }
+})();
diff --git a/web/viewer.js b/web/viewer.js
index b6b62af83..dd16b0282 100644
--- a/web/viewer.js
+++ b/web/viewer.js
@@ -6,6 +6,7 @@
 var kDefaultURL = 'compressed.tracemonkey-pldi-09.pdf';
 var kDefaultScale = 'auto';
 var kDefaultScaleDelta = 1.1;
+var kUnknownScale = 0;
 var kCacheSize = 20;
 var kCssUnits = 96.0 / 72.0;
 var kScrollbarPadding = 40;
@@ -148,7 +149,7 @@ var currentPageNumber = 1;
 var PDFView = {
   pages: [],
   thumbnails: [],
-  currentScale: 0,
+  currentScale: kUnknownScale,
   currentScaleValue: null,
   initialBookmark: document.location.hash.substring(1),
 
@@ -203,12 +204,12 @@ var PDFView = {
 
   zoomIn: function pdfViewZoomIn() {
     var newScale = Math.min(kMaxScale, this.currentScale * kDefaultScaleDelta);
-    this.setScale(newScale, true);
+    this.parseScale(newScale, true);
   },
 
   zoomOut: function pdfViewZoomOut() {
     var newScale = Math.max(kMinScale, this.currentScale / kDefaultScaleDelta);
-    this.setScale(newScale, true);
+    this.parseScale(newScale, true);
   },
 
   set page(val) {
@@ -452,10 +453,16 @@ var PDFView = {
     }
     else if (storedHash)
       this.setHash(storedHash);
-    else {
-      this.parseScale(scale || kDefaultScale, true);
+    else if (scale) {
+      this.parseScale(scale, true);
       this.page = 1;
     }
+
+    if (PDFView.currentScale === kUnknownScale) {
+      // Scale was not initialized: invalid bookmark or scale was not specified.
+      // Setting the default one.
+      this.parseScale(kDefaultScale, true);
+    }
   },
 
   setHash: function pdfViewSetHash(hash) {
@@ -742,6 +749,8 @@ var PageView = function pageView(container, content, id, pageWidth, pageHeight,
 
       if (scale && scale !== PDFView.currentScale)
         PDFView.parseScale(scale, true);
+      else if (PDFView.currentScale === kUnknownScale)
+        PDFView.parseScale(kDefaultScale, true);
 
       setTimeout(function pageViewScrollIntoViewRelayout() {
         // letting page to re-layout before scrolling
@@ -1267,7 +1276,7 @@ window.addEventListener('keydown', function keydown(evt) {
       handled = true;
       break;
     case 48: // '0'
-      PDFView.setScale(kDefaultScale, true);
+      PDFView.parseScale(kDefaultScale, true);
       handled = true;
       break;
     case 37: // left arrow