diff --git js/modal.js js/modal.js
index 94f4dc6..c53d534 100644
--- js/modal.js
+++ js/modal.js
@@ -76,15 +76,28 @@
         var width = Drupal.CTools.Modal.currentSettings.modalSize.width;
         var height = Drupal.CTools.Modal.currentSettings.modalSize.height;
       }
-
+      
+      var w_outer = width + Drupal.CTools.Modal.currentSettings.modalSize.addWidth + 'px';
+      var h_outer = height + Drupal.CTools.Modal.currentSettings.modalSize.addHeight + 'px';
+      var w_inner = (width - Drupal.CTools.Modal.currentSettings.modalSize.contentRight) + 'px';
+      var h_inner = (height - Drupal.CTools.Modal.currentSettings.modalSize.contentBottom) + 'px';
+      // if width / height is 'auto', dont add px and the current numeric size
+      // this e.g. will result in a unallowed CSS value which will crash jquery
+      // for IE
+      if(typeof width  == 'string') {
+        w_outer = w_inner = width;
+      }
+      if(typeof height == 'string') {
+        h_outer = h_inner = height;
+      }
       // Use the additionol pixels for creating the width and height.
       $('div.ctools-modal-content', context).css({
-        'width': width + Drupal.CTools.Modal.currentSettings.modalSize.addWidth + 'px',
-        'height': height + Drupal.CTools.Modal.currentSettings.modalSize.addHeight + 'px'
+        'width': w_outer,
+        'height': h_outer
       });
       $('div.ctools-modal-content .modal-content', context).css({
-        'width': (width - Drupal.CTools.Modal.currentSettings.modalSize.contentRight) + 'px',
-        'height': (height - Drupal.CTools.Modal.currentSettings.modalSize.contentBottom) + 'px'
+        'width': w_inner,
+        'height': h_inner
       });
     }