diff --git a/src/wp-includes/js/tinymce/plugins/wpeditimage/editor_plugin_src.js b/src/wp-includes/js/tinymce/plugins/wpeditimage/editor_plugin_src.js
index 17aa30e206..b26ed4a1a7 100644
--- a/src/wp-includes/js/tinymce/plugins/wpeditimage/editor_plugin_src.js
+++ b/src/wp-includes/js/tinymce/plugins/wpeditimage/editor_plugin_src.js
@@ -160,7 +160,8 @@
 				if ( cls == 'aligncenter' )
 					div_cls += ' mceIEcenter';
 
-				return '<div class="'+div_cls+'"><dl id="'+id+'" class="wp-caption '+cls+'" style="width: '+( 10 + parseInt(w) )+
+				w = parseInt( w, 10 ) + 10;
+				return '<div class="'+div_cls+'"><dl id="'+id+'" class="wp-caption '+cls+'" style="width: '+w+
 				'px"><dt class="wp-caption-dt">'+img+'</dt><dd class="wp-caption-dd">'+cap+'</dd></dl></div>';
 			});
 		},