diff --git a/components/dependency_injection/factories.rst b/components/dependency_injection/factories.rst
index 6727bc838a5..7a22ba17da2 100644
--- a/components/dependency_injection/factories.rst
+++ b/components/dependency_injection/factories.rst
@@ -68,6 +68,14 @@ class:
 
         $container->setDefinition('newsletter_manager', $definition);
 
+.. note::
+
+    When using a factory to create services, the value chosen for the ``class``
+    option has no effect on the resulting service. The actual class name only
+    depends on the object that is returned by the factory. However, the configured
+    class name may be used by compiler passes and therefore should be set to a
+    sensible value.
+
 When you specify the class to use for the factory (via ``factory_class``)
 the method will be called statically. If the factory itself should be instantiated
 and the resulting object's method called, configure the factory itself as a service.