diff --git a/core/modules/widgets/image.js b/core/modules/widgets/image.js
index 1c4ba494e..afa8b447b 100644
--- a/core/modules/widgets/image.js
+++ b/core/modules/widgets/image.js
@@ -97,10 +97,10 @@ ImageWidget.prototype.render = function(parent,nextSibling) {
 		domNode.setAttribute("class",this.imageClass);		
 	}
 	if(this.imageWidth) {
-		domNode.setAttribute("width",parseInt(this.imageWidth,10) + "px");
+		domNode.setAttribute("width",this.imageWidth);
 	}
 	if(this.imageHeight) {
-		domNode.setAttribute("height",parseInt(this.imageHeight,10) + "px");
+		domNode.setAttribute("height",this.imageHeight);
 	}
 	if(this.imageTooltip) {
 		domNode.setAttribute("title",this.imageTooltip);		
diff --git a/editions/tw5.com/tiddlers/widgets/ImageWidget.tid b/editions/tw5.com/tiddlers/widgets/ImageWidget.tid
index ebf65df72..dee19cadf 100644
--- a/editions/tw5.com/tiddlers/widgets/ImageWidget.tid
+++ b/editions/tw5.com/tiddlers/widgets/ImageWidget.tid
@@ -14,12 +14,14 @@ Any content of the `<$image>` widget is ignored.
 
 |!Attribute |!Description |
 |source |The URL of the image, or the title of an image tiddler |
-|width |The width of the image as a number |
+|width |The width of the image |
 |height |The height of the image |
 |tooltip |The tooltip to be displayed over the image |
 |alt |The alternative text to be associated with the image |
 |class |CSS classes to be assigned to the `<img>` element |
 
+The width and the height can be specified as pixel values (eg "23" or "23px") or percentages (eg "23%"). They are both optional; if not provided the browser will use CSS rules to size the image.
+
 ! External Images and the ''_canonical_uri'' field
 
 When used to display tiddler-based images, the image widget operates in two distinct modes: