diff --git src/wp-admin/includes/schema.php src/wp-admin/includes/schema.php
index 64ec6b7..a32b85c 100644
--- src/wp-admin/includes/schema.php
+++ src/wp-admin/includes/schema.php
@@ -242,8 +242,8 @@
 
 	// Multisite global tables.
 	$ms_global_tables = "CREATE TABLE $wpdb->blogs (
-  blog_id bigint(20) NOT NULL auto_increment,
-  site_id bigint(20) NOT NULL default '0',
+  blog_id bigint(20) unsigned NOT NULL auto_increment,
+  site_id bigint(20) unsigned NOT NULL default '0',
   domain varchar(200) NOT NULL default '',
   path varchar(100) NOT NULL default '',
   registered datetime NOT NULL default '0000-00-00 00:00:00',
@@ -259,31 +259,31 @@
   KEY lang_id (lang_id)
 ) $charset_collate;
 CREATE TABLE $wpdb->blog_versions (
-  blog_id bigint(20) NOT NULL default '0',
+  blog_id bigint(20) unsigned NOT NULL default '0',
   db_version varchar(20) NOT NULL default '',
   last_updated datetime NOT NULL default '0000-00-00 00:00:00',
   PRIMARY KEY  (blog_id),
   KEY db_version (db_version)
 ) $charset_collate;
 CREATE TABLE $wpdb->registration_log (
-  ID bigint(20) NOT NULL auto_increment,
+  ID bigint(20) unsigned NOT NULL auto_increment,
   email varchar(255) NOT NULL default '',
   IP varchar(30) NOT NULL default '',
-  blog_id bigint(20) NOT NULL default '0',
+  blog_id bigint(20) unsigned NOT NULL default '0',
   date_registered datetime NOT NULL default '0000-00-00 00:00:00',
   PRIMARY KEY  (ID),
   KEY IP (IP)
 ) $charset_collate;
 CREATE TABLE $wpdb->site (
-  id bigint(20) NOT NULL auto_increment,
+  id bigint(20) unsigned NOT NULL auto_increment,
   domain varchar(200) NOT NULL default '',
   path varchar(100) NOT NULL default '',
   PRIMARY KEY  (id),
   KEY domain (domain(140),path(51))
 ) $charset_collate;
 CREATE TABLE $wpdb->sitemeta (
-  meta_id bigint(20) NOT NULL auto_increment,
-  site_id bigint(20) NOT NULL default '0',
+  meta_id bigint(20) unsigned NOT NULL auto_increment,
+  site_id bigint(20) unsigned NOT NULL default '0',
   meta_key varchar(255) default NULL,
   meta_value longtext,
   PRIMARY KEY  (meta_id),
@@ -291,7 +291,7 @@
   KEY site_id (site_id)
 ) $charset_collate;
 CREATE TABLE $wpdb->signups (
-  signup_id bigint(20) NOT NULL auto_increment,
+  signup_id bigint(20) unsigned NOT NULL auto_increment,
   domain varchar(200) NOT NULL default '',
   path varchar(100) NOT NULL default '',
   title longtext NOT NULL,
diff --git src/wp-admin/includes/upgrade.php src/wp-admin/includes/upgrade.php
index 94ad771..7f5a8a3 100644
--- src/wp-admin/includes/upgrade.php
+++ src/wp-admin/includes/upgrade.php
@@ -2834,6 +2834,20 @@
 			$wpdb->query( "ALTER TABLE $wpdb->blogs CHANGE COLUMN archived archived varchar(1) NOT NULL default '0'" );
 			$wpdb->query( "ALTER TABLE $wpdb->blogs CHANGE COLUMN archived archived tinyint(2) NOT NULL default 0" );
 		}
+
+		// Upgrade versions prior to 4.8
+		if ( $wp_current_db_version < 39357 ) {
+			// Convert ID columns from signed to unsigned
+			$wpdb->query( "ALTER TABLE $wpdb->blogs MODIFY blog_id bigint(20) unsigned NOT NULL auto_increment" );
+			$wpdb->query( "ALTER TABLE $wpdb->blogs MODIFY site_id bigint(20) unsigned NOT NULL default 0" );
+			$wpdb->query( "ALTER TABLE $wpdb->blog_versions MODIFY blog_id bigint(20) unsigned NOT NULL default 0" );
+			$wpdb->query( "ALTER TABLE $wpdb->registration_log MODIFY ID bigint(20) unsigned NOT NULL auto_increment" );
+			$wpdb->query( "ALTER TABLE $wpdb->registration_log MODIFY blog_id bigint(20) unsigned NOT NULL default 0" );
+			$wpdb->query( "ALTER TABLE $wpdb->site MODIFY id bigint(20) unsigned NOT NULL auto_increment" );
+			$wpdb->query( "ALTER TABLE $wpdb->sitemeta MODIFY meta_id bigint(20) unsigned NOT NULL auto_increment" );
+			$wpdb->query( "ALTER TABLE $wpdb->sitemeta MODIFY site_id bigint(20) unsigned NOT NULL default 0" );
+			$wpdb->query( "ALTER TABLE $wpdb->signups MODIFY signup_id bigint(20) unsigned NOT NULL auto_increment" );
+		}
 	}
 
 	// Upgrade versions prior to 4.2.
diff --git src/wp-includes/version.php src/wp-includes/version.php
index e01c790..20ca436 100644
--- src/wp-includes/version.php
+++ src/wp-includes/version.php
@@ -11,7 +11,7 @@
  *
  * @global int $wp_db_version
  */
-$wp_db_version = 38590;
+$wp_db_version = 39357;
 
 /**
  * Holds the TinyMCE version