diff --git a/tests/RUNNING_TESTS.txt b/tests/RUNNING_TESTS.txt
index 7c2a7c3fce..95c6b0a057 100644
--- a/tests/RUNNING_TESTS.txt
+++ b/tests/RUNNING_TESTS.txt
@@ -17,7 +17,24 @@ PHP extensions
 Unit tests use several PHP extensions that board code does not use. Currently
 the following PHP extensions must be installed and enabled to run unit tests:
 
-- ctype
+- ctype (also a phpunit dependency)
+- dom (phpunit dependency)
+
+Some of the functionality in phpBB and/or the test suite uses additional
+PHP extensions. If these extensions are not loaded, respective tests
+will be skipped:
+
+- apc (APC cache driver)
+- bz2 (compress tests)
+- interbase, pdo_firebird (Firebird database driver)
+- mysql, pdo_mysql (MySQL database driver)
+- mysqli, pdo_mysql (MySQLi database driver)
+- pdo (any database tests)
+- pgsql, pdo_pgsql (PostgreSQL database driver)
+- simplexml (any database tests)
+- sqlite, pdo_sqlite (SQLite database driver, requires SQLite 2.x support
+  in pdo_sqlite)
+- zlib (compress tests)
 
 Database Tests
 --------------