diff --git a/phpunit.xml.all b/phpunit.xml.all
new file mode 100644
index 0000000000..1be2830729
--- /dev/null
+++ b/phpunit.xml.all
@@ -0,0 +1,25 @@
+<?xml version="1.0" encoding="UTF-8"?>
+
+<phpunit backupGlobals="true"
+         backupStaticAttributes="true"
+         colors="true"
+         convertErrorsToExceptions="true"
+         convertNoticesToExceptions="true"
+         convertWarningsToExceptions="true"
+         processIsolation="false"
+         stopOnFailure="false"
+         syntaxCheck="false"
+         bootstrap="tests/bootstrap.php"
+>
+    <testsuites>
+        <testsuite name="phpBB Test Suite">
+            <directory suffix="_test.php">./tests/</directory>
+        </testsuite>
+    </testsuites>
+
+    <filter>
+        <blacklist>
+            <directory>./tests/</directory>
+        </blacklist>
+    </filter>
+</phpunit>
diff --git a/tests/RUNNING_TESTS.txt b/tests/RUNNING_TESTS.txt
index ac07978d3e..59197acc0f 100644
--- a/tests/RUNNING_TESTS.txt
+++ b/tests/RUNNING_TESTS.txt
@@ -50,6 +50,15 @@ Once the prerequisites are installed, run the tests from the project root direct
 
     $ phpunit
 
+Slow tests
+--------------
+Certain tests, such as the UTF-8 normalizer or the DNS tests tend to be slow.
+Thus these tests are in the `slow` group, which is excluded by default. You can
+enable slow tests by copying the phpunit.xml.all file to phpunit.xml. If you only
+want the slow tests, run:
+
+    $ phpunit --group slow
+
 More Information
 ================