Index: wp-admin/admin-header.php
===================================================================
--- wp-admin/admin-header.php	(revision 8013)
+++ wp-admin/admin-header.php	(working copy)
@@ -87,7 +87,7 @@
 	<a href="http://gears.google.com/" target="_blank" style="font-weight:normal;"><?php _e('More information...'); ?></a></p>
 	<p><?php _e('After installing and enabling it, most of the WordPress images, scripts and CSS files will be stored on this computer. This will speed up page loading.'); ?></p>
 	<p><strong><?php _e('Please make sure you are not using a public or shared computer.'); ?></strong></p>
-	<div class="submit"><button onclick="window.location = 'http://gears.google.com/?action=install&return=<?php echo admin_url() ?>';" class="button"><?php _e('Install Now'); ?></button>
+	<div class="submit"><button onclick="window.location = 'http://gears.google.com/?action=install&amp;return=<?php echo urlencode( admin_url() ); ?>';" class="button"><?php _e('Install Now'); ?></button>
 	<button class="button" style="margin-left:10px;" onclick="document.getElementById('gears-info-box').style.display='none';">Cancel</button></div>
 	</div>