Index: /CKEditor/trunk/CHANGES.html
===================================================================
--- /CKEditor/trunk/CHANGES.html	(revision 5383)
+++ /CKEditor/trunk/CHANGES.html	(revision 5384)
@@ -146,4 +146,5 @@
 		<li><a href="http://dev.fckeditor.net/ticket/4476">#4476</a> : [IE] Inaccessible empty list item contains sub list.</li>
 		<li><a href="http://dev.fckeditor.net/ticket/4881">#4881</a> : [IE] Selection range broken because of cutting a single control type element from it.</li>
+		<li><a href="http://dev.fckeditor.net/ticket/5505">#5505</a> : Image dialog throw JavaScript error when click close dialog before preview area is loading.</li>
 		<li>Updated the following language files:<ul>
 			<li><a href="http://dev.fckeditor.net/ticket/5326">#5326</a> : Catalan;</li>
Index: /CKEditor/trunk/_source/plugins/image/dialogs/image.js
===================================================================
--- /CKEditor/trunk/_source/plugins/image/dialogs/image.js	(revision 5383)
+++ /CKEditor/trunk/_source/plugins/image/dialogs/image.js	(revision 5384)
@@ -114,6 +114,11 @@
 	var switchLockRatio = function( dialog, value )
 	{
-		var oImageOriginal = dialog.originalElement,
-			ratioButton = CKEDITOR.document.getById( 'btnLockSizes' );
+		var oImageOriginal = dialog.originalElement;
+
+		// Dialog may already closed. (#5505)
+		if( !oImageOriginal )
+			return;
+
+		var ratioButton = CKEDITOR.document.getById( 'btnLockSizes' );
 
 		if ( oImageOriginal.getCustomData( 'isReady' ) == 'true' )