diff --git a/themes/base/images/ui-bg_diagonals-thick_20_666666_40x40.png b/themes/base/images/ui-bg_diagonals-thick_20_666666_40x40.png
new file mode 100755
index 00000000000..64ece5707d9
Binary files /dev/null and b/themes/base/images/ui-bg_diagonals-thick_20_666666_40x40.png differ
diff --git a/themes/base/jquery.ui.progressbar.css b/themes/base/jquery.ui.progressbar.css
index e24afc88681..effcfeb9d3f 100644
--- a/themes/base/jquery.ui.progressbar.css
+++ b/themes/base/jquery.ui.progressbar.css
@@ -8,4 +8,28 @@
  * http://docs.jquery.com/UI/Progressbar#theming
  */
 .ui-progressbar { height:2em; text-align: left; overflow: hidden; }
-.ui-progressbar .ui-progressbar-value {margin: -1px; height:100%; }
\ No newline at end of file
+.ui-progressbar .ui-progressbar-value { margin: -1px; height:100%; }
+@-webkit-keyframes bg-anim {
+    from { background-position: 0 0 }
+    to { background-position: 40px 0 }
+}
+@-moz-keyframes bg-anim {
+    from { background-position: 0 0 }
+    to { background-position: 40px 0 }
+}
+@-ms-keyframes bg-anim {
+    from { background-position: 0 0 }
+    to { background-position: 40px 0 }
+}
+@keyframes bg-anim {
+    from { background-position: 0 0 }
+    to { background-position: 40px 0 }
+}
+
+.ui-progressbar .ui-progressbar-indeterminate {
+    background: url("images/ui-bg_diagonals-thick_20_666666_40x40.png");
+    -webkit-animation: bg-anim 1s linear infinite;
+    -moz-animation: bg-anim 1s linear infinite;
+    -ms-animation: bg-anim 1s linear infinite;
+    animation: bg-anim 1s linear infinite;
+}
diff --git a/ui/jquery.ui.progressbar.js b/ui/jquery.ui.progressbar.js
index 26f5e76f0e8..b268497bd1f 100644
--- a/ui/jquery.ui.progressbar.js
+++ b/ui/jquery.ui.progressbar.js
@@ -23,13 +23,13 @@ $.widget( "ui.progressbar", {
 	min: 0,
 
 	_create: function() {
+		var val = this._value();
 		this.element
 			.addClass( "ui-progressbar ui-widget ui-widget-content ui-corner-all" )
 			.attr({
 				role: "progressbar",
 				"aria-valuemin": this.min,
-				"aria-valuemax": this.options.max,
-				"aria-valuenow": this._value()
+				"aria-valuemax": this.options.max
 			});
 
 		this.valueDiv = $( "<div class='ui-progressbar-value ui-widget-header ui-corner-left'></div>" )
@@ -74,30 +74,39 @@ $.widget( "ui.progressbar", {
 	_value: function() {
 		var val = this.options.value;
 		// normalize invalid value
-		if ( typeof val !== "number" ) {
+		if ( typeof val !== "number" && val !== false ) {
 			val = 0;
+		} else if( val === false ) {
+			val = NaN;
 		}
 		return Math.min( this.options.max, Math.max( this.min, val ) );
 	},
 
 	_percentage: function() {
-		return 100 * this._value() / this.options.max;
+		var val = this._value();
+		return isNaN( val ) ? 100 : 100 * val / this.options.max;
 	},
 
 	_refreshValue: function() {
 		var value = this.value();
 		var percentage = this._percentage();
 
-		if ( this.oldValue !== value ) {
+		this.valueDiv.toggleClass( "ui-progressbar-indeterminate", isNaN( value ) );
+
+		if ( this.oldValue !== value && ( !isNaN( this.oldValue ) || !isNaN( value ) ) ) {
 			this.oldValue = value;
 			this._trigger( "change" );
 		}
 
 		this.valueDiv
-			.toggle( value > this.min )
+			.toggle( isNaN( value ) || value > this.min )
 			.toggleClass( "ui-corner-right", value === this.options.max )
 			.width( percentage.toFixed(0) + "%" );
-		this.element.attr( "aria-valuenow", value );
+		if ( isNaN( value ) ) {
+			this.element.removeAttr( "aria-valuenow" );
+		} else {
+			this.element.attr( "aria-valuenow", value );
+		}
 	}
 });