diff --git a/docs/simplesamlphp-install.md b/docs/simplesamlphp-install.md
index 1f127a549fced03ee53f494b1033753f669c07a8..0c4ba9c4859687b7954f1228e4e023abf71a5777 100644
--- a/docs/simplesamlphp-install.md
+++ b/docs/simplesamlphp-install.md
@@ -33,7 +33,7 @@ Prerequisites
  * Some webserver capable of executing PHP scripts.
  * PHP version >= 5.4.0.
  * Support for the following PHP extensions:
-   * Always required: `date`, `dom`, `hash`, `libxml`, `openssl`, `pcre`, `SPL`, `zlib`, `json`
+   * Always required: `date`, `dom`, `hash`, `libxml`, `openssl`, `pcre`, `SPL`, `zlib`, `json`, `mbstring`
    * When automatically checking for latest versions, and used by some modules: `cURL`
    * When authenticating against LDAP server: `ldap`
    * When authenticating against RADIUS server: `radius`