Index: src/wp-includes/ms-functions.php
===================================================================
--- src/wp-includes/ms-functions.php	(revision 38433)
+++ src/wp-includes/ms-functions.php	(working copy)
@@ -109,15 +109,14 @@
  * The count is cached and updated twice daily. This is not a live count.
  *
  * @since MU 1.0
+ * @since 3.7.0 The $network_id parameter has been deprecated.
+ * @since 4.7.0 The $network_id parameter is now being used.
  *
- * @param int $network_id Deprecated, not supported.
+ * @param int $network_id ID of the network. Can be null to default to the current network ID. Default null.
  * @return int
  */
-function get_blog_count( $network_id = 0 ) {
-	if ( func_num_args() )
-		_deprecated_argument( __FUNCTION__, '3.1.0' );
-
-	return get_site_option( 'blog_count' );
+function get_blog_count( $network_id = null ) {
+	return get_network_option( $network_id, 'blog_count' );
 }
 
 /**