Index: wp-admin/options-discussion.php
===================================================================
--- wp-admin/options-discussion.php	(revision 7886)
+++ wp-admin/options-discussion.php	(working copy)
@@ -135,7 +135,7 @@
 	$avatar_list .= "\n\t<label><input type='radio' name='avatar_default' id='avatar_{$default_key}' value='{$default_key}' {$selected}/> ";
 
 	$avatar = get_avatar( $user_email, $size, $default_key );
-	$avatar_list .= preg_replace("/src='(.+?)'/", "src='\$1&amp;forcedefault=1'", $avatar);
+	$avatar_list .= preg_replace('/src="(.+?)"/', "src='\$1&amp;forcedefault=1'", $avatar);
 
 	$avatar_list .= ' ' . $default_name . '</label>';
 	$avatar_list .= '<br />';