Index: wp-includes/pluggable.php
===================================================================
--- wp-includes/pluggable.php	(revision 7091)
+++ wp-includes/pluggable.php	(working copy)
@@ -1207,13 +1207,12 @@
 
 	if ( empty($default) )
 		$default = "http://www.gravatar.com/avatar.php?gravatar_id=ad516503a11cd5ca435acc9bb6523536&size=$size"; // ad516503a11cd5ca435acc9bb6523536 == md5('unknown@gravatar.com')
-	$default = urlencode( $default );
 
 	if ( !empty($email) ) {
 		$out = 'http://www.gravatar.com/avatar.php?gravatar_id=';
 		$out .= md5( strtolower( $email ) );
 		$out .= "&size={$size}";
-		$out .= "&default={$default}";
+		$out .= '&default=' . urlencode( $default );
 
 		$rating = get_option('avatar_rating');
 		if ( !empty( $rating ) )