diff --git a/INSTALL b/INSTALL
index 0483320a78..bddeb41b18 100644
--- a/INSTALL
+++ b/INSTALL
@@ -41,6 +41,7 @@ functional setup of GNU Social:
 - php5-curl     Fetching files by HTTP.
 - php5-gd       Image manipulation (scaling).
 - php5-gmp      For Salmon signatures (part of OStatus).
+- php5-intl     Internationalization support, part of core.
 - php5-json     For WebFinger lookups and more.
 - php5-mysqlnd  The native driver for PHP5 MariaDB connections. If you
                   use MySQL, 'mysql' or 'mysqli' may work.