diff --git a/build/iscroll-infinite.js b/build/iscroll-infinite.js
index 0c22c7e6..10170f69 100644
--- a/build/iscroll-infinite.js
+++ b/build/iscroll-infinite.js
@@ -1,4 +1,4 @@
-/*! iScroll v5.1.2 ~ (c) 2008-2014 Matteo Spinelli ~ http://cubiq.org/license */
+/*! iScroll v5.1.3 ~ (c) 2008-2014 Matteo Spinelli ~ http://cubiq.org/license */
 (function (window, document, Math) {
 var rAF = window.requestAnimationFrame	||
 	window.webkitRequestAnimationFrame	||
@@ -337,7 +337,7 @@ function IScroll (el, options) {
 }
 
 IScroll.prototype = {
-	version: '5.1.2',
+	version: '5.1.3',
 
 	_init: function () {
 		this._initEvents();
@@ -941,8 +941,13 @@ IScroll.prototype = {
 		}, 400);
 
 		if ( 'deltaX' in e ) {
-			wheelDeltaX = -e.deltaX;
-			wheelDeltaY = -e.deltaY;
+			if (e.deltaMode === 1) {
+				wheelDeltaX = -e.deltaX * this.options.mouseWheelSpeed;
+				wheelDeltaY = -e.deltaY * this.options.mouseWheelSpeed;
+			} else {
+				wheelDeltaX = -e.deltaX;
+				wheelDeltaY = -e.deltaY;
+			}
 		} else if ( 'wheelDeltaX' in e ) {
 			wheelDeltaX = e.wheelDeltaX / 120 * this.options.mouseWheelSpeed;
 			wheelDeltaY = e.wheelDeltaY / 120 * this.options.mouseWheelSpeed;
diff --git a/build/iscroll-lite.js b/build/iscroll-lite.js
index 749cc01c..bd143b79 100644
--- a/build/iscroll-lite.js
+++ b/build/iscroll-lite.js
@@ -1,4 +1,4 @@
-/*! iScroll v5.1.2 ~ (c) 2008-2014 Matteo Spinelli ~ http://cubiq.org/license */
+/*! iScroll v5.1.3 ~ (c) 2008-2014 Matteo Spinelli ~ http://cubiq.org/license */
 (function (window, document, Math) {
 var rAF = window.requestAnimationFrame	||
 	window.webkitRequestAnimationFrame	||
@@ -320,7 +320,7 @@ function IScroll (el, options) {
 }
 
 IScroll.prototype = {
-	version: '5.1.2',
+	version: '5.1.3',
 
 	_init: function () {
 		this._initEvents();
diff --git a/build/iscroll-probe.js b/build/iscroll-probe.js
index 76456c40..538d0e38 100644
--- a/build/iscroll-probe.js
+++ b/build/iscroll-probe.js
@@ -1,4 +1,4 @@
-/*! iScroll v5.1.2 ~ (c) 2008-2014 Matteo Spinelli ~ http://cubiq.org/license */
+/*! iScroll v5.1.3 ~ (c) 2008-2014 Matteo Spinelli ~ http://cubiq.org/license */
 (function (window, document, Math) {
 var rAF = window.requestAnimationFrame	||
 	window.webkitRequestAnimationFrame	||
@@ -335,7 +335,7 @@ function IScroll (el, options) {
 }
 
 IScroll.prototype = {
-	version: '5.1.2',
+	version: '5.1.3',
 
 	_init: function () {
 		this._initEvents();
@@ -1063,8 +1063,13 @@ IScroll.prototype = {
 		}, 400);
 
 		if ( 'deltaX' in e ) {
-			wheelDeltaX = -e.deltaX;
-			wheelDeltaY = -e.deltaY;
+			if (e.deltaMode === 1) {
+				wheelDeltaX = -e.deltaX * this.options.mouseWheelSpeed;
+				wheelDeltaY = -e.deltaY * this.options.mouseWheelSpeed;
+			} else {
+				wheelDeltaX = -e.deltaX;
+				wheelDeltaY = -e.deltaY;
+			}
 		} else if ( 'wheelDeltaX' in e ) {
 			wheelDeltaX = e.wheelDeltaX / 120 * this.options.mouseWheelSpeed;
 			wheelDeltaY = e.wheelDeltaY / 120 * this.options.mouseWheelSpeed;
diff --git a/build/iscroll-zoom.js b/build/iscroll-zoom.js
index bd803c6c..4faccdfc 100644
--- a/build/iscroll-zoom.js
+++ b/build/iscroll-zoom.js
@@ -1,4 +1,4 @@
-/*! iScroll v5.1.2 ~ (c) 2008-2014 Matteo Spinelli ~ http://cubiq.org/license */
+/*! iScroll v5.1.3 ~ (c) 2008-2014 Matteo Spinelli ~ http://cubiq.org/license */
 (function (window, document, Math) {
 var rAF = window.requestAnimationFrame	||
 	window.webkitRequestAnimationFrame	||
@@ -337,7 +337,7 @@ function IScroll (el, options) {
 }
 
 IScroll.prototype = {
-	version: '5.1.2',
+	version: '5.1.3',
 
 	_init: function () {
 		this._initEvents();
@@ -1227,8 +1227,13 @@ IScroll.prototype = {
 		}, 400);
 
 		if ( 'deltaX' in e ) {
-			wheelDeltaX = -e.deltaX;
-			wheelDeltaY = -e.deltaY;
+			if (e.deltaMode === 1) {
+				wheelDeltaX = -e.deltaX * this.options.mouseWheelSpeed;
+				wheelDeltaY = -e.deltaY * this.options.mouseWheelSpeed;
+			} else {
+				wheelDeltaX = -e.deltaX;
+				wheelDeltaY = -e.deltaY;
+			}
 		} else if ( 'wheelDeltaX' in e ) {
 			wheelDeltaX = e.wheelDeltaX / 120 * this.options.mouseWheelSpeed;
 			wheelDeltaY = e.wheelDeltaY / 120 * this.options.mouseWheelSpeed;
diff --git a/build/iscroll.js b/build/iscroll.js
index 32b1ad5b..8bd2b8da 100644
--- a/build/iscroll.js
+++ b/build/iscroll.js
@@ -1,4 +1,4 @@
-/*! iScroll v5.1.2 ~ (c) 2008-2014 Matteo Spinelli ~ http://cubiq.org/license */
+/*! iScroll v5.1.3 ~ (c) 2008-2014 Matteo Spinelli ~ http://cubiq.org/license */
 (function (window, document, Math) {
 var rAF = window.requestAnimationFrame	||
 	window.webkitRequestAnimationFrame	||
@@ -332,7 +332,7 @@ function IScroll (el, options) {
 }
 
 IScroll.prototype = {
-	version: '5.1.2',
+	version: '5.1.3',
 
 	_init: function () {
 		this._initEvents();
@@ -1054,8 +1054,13 @@ IScroll.prototype = {
 		}, 400);
 
 		if ( 'deltaX' in e ) {
-			wheelDeltaX = -e.deltaX;
-			wheelDeltaY = -e.deltaY;
+			if (e.deltaMode === 1) {
+				wheelDeltaX = -e.deltaX * this.options.mouseWheelSpeed;
+				wheelDeltaY = -e.deltaY * this.options.mouseWheelSpeed;
+			} else {
+				wheelDeltaX = -e.deltaX;
+				wheelDeltaY = -e.deltaY;
+			}
 		} else if ( 'wheelDeltaX' in e ) {
 			wheelDeltaX = e.wheelDeltaX / 120 * this.options.mouseWheelSpeed;
 			wheelDeltaY = e.wheelDeltaY / 120 * this.options.mouseWheelSpeed;
diff --git a/package.json b/package.json
index f74fa114..90be17e4 100644
--- a/package.json
+++ b/package.json
@@ -1,7 +1,7 @@
 {
   "name": "iscroll",
   "description": "Smooth scrolling for the web",
-  "version": "5.1.2",
+  "version": "5.1.3",
   "homepage": "http://cubiq.org/iscroll-4",
   "author": "Matteo Spinelli <matteo@cubiq.org> (http://cubiq.org)",
   "keywords": [