Index: src/wp-admin/includes/upgrade.php
===================================================================
--- src/wp-admin/includes/upgrade.php	(revision 33594)
+++ src/wp-admin/includes/upgrade.php	(working copy)
@@ -1685,6 +1685,11 @@
 
 			$tables = $wpdb->tables( 'global' );
 
+			// sitecategories may not exist.
+			if ( ! $this->get_var( "SHOW TABLES LIKE '{$tables['sitecategories']}'" ) ) {
+				unset( $tables['sitecategories'] );
+			}
+
 			foreach ( $tables as $table ) {
 				maybe_convert_table_to_utf8mb4( $table );
 			}
@@ -1709,6 +1714,11 @@
 
 			$tables = $wpdb->tables( 'global' );
 
+			// sitecategories may not exist.
+			if ( ! $this->get_var( "SHOW TABLES LIKE '{$tables['sitecategories']}'" ) ) {
+				unset( $tables['sitecategories'] );
+			}
+
 			foreach ( $tables as $table ) {
 				maybe_convert_table_to_utf8mb4( $table );
 			}