diff --git a/bower.json b/bower.json
index 8c033a4de..fa6f8d3ca 100644
--- a/bower.json
+++ b/bower.json
@@ -1,6 +1,6 @@
 {
   "name": "pdfjs-dist",
-  "version": "1.5.490",
+  "version": "1.5.492",
   "main": [
     "build/pdf.js",
     "build/pdf.worker.js"
diff --git a/build/pdf.combined.js b/build/pdf.combined.js
index 70941376c..042ad36b4 100644
--- a/build/pdf.combined.js
+++ b/build/pdf.combined.js
@@ -28,8 +28,8 @@ factory((root.pdfjsDistBuildPdfCombined = {}));
   // Use strict in our context only - users might not want it
   'use strict';
 
-var pdfjsVersion = '1.5.490';
-var pdfjsBuild = '7f381c8';
+var pdfjsVersion = '1.5.492';
+var pdfjsBuild = 'a9a3396';
 
   var pdfjsFilePath =
     typeof document !== 'undefined' && document.currentScript ?
diff --git a/build/pdf.js b/build/pdf.js
index de78b034f..c97b82e4c 100644
--- a/build/pdf.js
+++ b/build/pdf.js
@@ -28,8 +28,8 @@ factory((root.pdfjsDistBuildPdf = {}));
   // Use strict in our context only - users might not want it
   'use strict';
 
-var pdfjsVersion = '1.5.490';
-var pdfjsBuild = '7f381c8';
+var pdfjsVersion = '1.5.492';
+var pdfjsBuild = 'a9a3396';
 
   var pdfjsFilePath =
     typeof document !== 'undefined' && document.currentScript ?
diff --git a/build/pdf.worker.js b/build/pdf.worker.js
index 8bd8daf37..be1bb8e41 100644
--- a/build/pdf.worker.js
+++ b/build/pdf.worker.js
@@ -28,8 +28,8 @@ factory((root.pdfjsDistBuildPdfWorker = {}));
   // Use strict in our context only - users might not want it
   'use strict';
 
-var pdfjsVersion = '1.5.490';
-var pdfjsBuild = '7f381c8';
+var pdfjsVersion = '1.5.492';
+var pdfjsBuild = 'a9a3396';
 
   var pdfjsFilePath =
     typeof document !== 'undefined' && document.currentScript ?
diff --git a/package.json b/package.json
index 3e289f199..d22d08052 100644
--- a/package.json
+++ b/package.json
@@ -1,6 +1,6 @@
 {
   "name": "pdfjs-dist",
-  "version": "1.5.490",
+  "version": "1.5.492",
   "main": "build/pdf.js",
   "description": "Generic build of Mozilla's PDF.js library.",
   "keywords": [
diff --git a/web/pdf_viewer.js b/web/pdf_viewer.js
index dfaffe118..5a39cb98d 100644
--- a/web/pdf_viewer.js
+++ b/web/pdf_viewer.js
@@ -658,6 +658,28 @@ function getPDFFileNameFromURL(url) {
   return suggestedFilename || 'document.pdf';
 }
 
+function normalizeWheelEventDelta(evt) {
+  var delta = Math.sqrt(evt.deltaX * evt.deltaX + evt.deltaY * evt.deltaY);
+  var angle = Math.atan2(evt.deltaY, evt.deltaX);
+  if (-0.25 * Math.PI < angle && angle < 0.75 * Math.PI) {
+    // All that is left-up oriented has to change the sign.
+    delta = -delta;
+  }
+
+  var MOUSE_DOM_DELTA_PIXEL_MODE = 0;
+  var MOUSE_DOM_DELTA_LINE_MODE = 1;
+  var MOUSE_PIXELS_PER_LINE = 30;
+  var MOUSE_LINES_PER_PAGE = 30;
+
+  // Converts delta to per-page units
+  if (evt.deltaMode === MOUSE_DOM_DELTA_PIXEL_MODE) {
+    delta /= MOUSE_PIXELS_PER_LINE * MOUSE_LINES_PER_PAGE;
+  } else if (evt.deltaMode === MOUSE_DOM_DELTA_LINE_MODE) {
+    delta /= MOUSE_LINES_PER_PAGE;
+  }
+  return delta;
+}
+
 /**
  * Simple event bus for an application. Listeners are attached using the
  * `on` and `off` methods. To raise an event, the `dispatch` method shall be
@@ -803,6 +825,7 @@ exports.getOutputScale = getOutputScale;
 exports.scrollIntoView = scrollIntoView;
 exports.watchScroll = watchScroll;
 exports.binarySearchFirstItem = binarySearchFirstItem;
+exports.normalizeWheelEventDelta = normalizeWheelEventDelta;
 }));