diff --git a/phpBB/includes/functions.php b/phpBB/includes/functions.php
index 571c863839..ccd2d3147c 100644
--- a/phpBB/includes/functions.php
+++ b/phpBB/includes/functions.php
@@ -137,7 +137,18 @@ function request_var($var_name, $default, $multibyte = false, $cookie = false)
 }
 
 /**
-* Set config value. Creates missing config entry.
+* Sets a configuration option's value.
+*
+* Please note that this function does not update the is_dynamic value for
+* an already existing config option.
+*
+* @param string $config_name   The configuration option's name
+* @param string $config_value  New configuration value
+* @param bool   $is_dynamic    Whether this variable should be cached (false) or
+*                              if it changes too frequently (true) to be
+*                              efficiently cached.
+*
+* @return null
 */
 function set_config($config_name, $config_value, $is_dynamic = false)
 {
@@ -166,7 +177,15 @@ function set_config($config_name, $config_value, $is_dynamic = false)
 }
 
 /**
-* Set dynamic config value with arithmetic operation.
+* Increments an integer config value directly in the database.
+*
+* @param string $config_name   The configuration option's name
+* @param int    $increment     Amount to increment by
+* @param bool   $is_dynamic    Whether this variable should be cached (false) or
+*                              if it changes too frequently (true) to be
+*                              efficiently cached.
+*
+* @return null
 */
 function set_config_count($config_name, $increment, $is_dynamic = false)
 {