Index: wp-includes/pluggable.php
===================================================================
--- wp-includes/pluggable.php	(revision 22339)
+++ wp-includes/pluggable.php	(working copy)
@@ -1637,23 +1637,25 @@
 			$host = 'http://0.gravatar.com';
 	}
 
+	$retina = $size * 2;
+
 	if ( 'mystery' == $default )
-		$default = "$host/avatar/ad516503a11cd5ca435acc9bb6523536?s={$size}"; // ad516503a11cd5ca435acc9bb6523536 == md5('unknown@gravatar.com')
+		$default = "$host/avatar/ad516503a11cd5ca435acc9bb6523536?s={$retina}"; // ad516503a11cd5ca435acc9bb6523536 == md5('unknown@gravatar.com')
 	elseif ( 'blank' == $default )
 		$default = includes_url('images/blank.gif');
 	elseif ( !empty($email) && 'gravatar_default' == $default )
 		$default = '';
 	elseif ( 'gravatar_default' == $default )
-		$default = "$host/avatar/?s={$size}";
+		$default = "$host/avatar/?s={$retina}";
 	elseif ( empty($email) )
-		$default = "$host/avatar/?d=$default&s={$size}";
+		$default = "$host/avatar/?d=$default&s={$retina}";
 	elseif ( strpos($default, 'http://') === 0 )
-		$default = add_query_arg( 's', $size, $default );
+		$default = add_query_arg( 's', $retina, $default );
 
 	if ( !empty($email) ) {
 		$out = "$host/avatar/";
 		$out .= $email_hash;
-		$out .= '?s='.$size;
+		$out .= '?s='.$retina;
 		$out .= '&d=' . urlencode( $default );
 
 		$rating = get_option('avatar_rating');