diff --git a/docs/src/main/asciidoc/functional.adoc b/docs/src/main/asciidoc/functional.adoc
index 284df4ac4..60c54ba98 100644
--- a/docs/src/main/asciidoc/functional.adoc
+++ b/docs/src/main/asciidoc/functional.adoc
@@ -94,6 +94,8 @@ It would also work if you add a separate, standalone class of type `Function` an
 
 The app runs in its own HTTP server if you add `spring-cloud-starter-function-webflux` (it won't work with the MVC starter at the moment because the functional form of the embedded Servlet container hasn't been implemented).  The app also runs just fine in AWS Lambda or Azure Functions, and the improvements in startup time are dramatic.
 
+NOTE: The "lite" web server has some limitations for the range of `Function` signatures - in particular it doesn't (yet) support `Message` input and output, but POJOs and any kind of `Publisher` should be fine.
+
 == Testing Functional Applications
 
 Spring Cloud Function also has some utilities for integration testing that will be very familiar to Spring Boot users. For example, here is an integration test for the HTTP server wrapping the app above:
@@ -142,4 +144,4 @@ public class FunctionalTests {
 
 == Limitations of Functional Bean Declaration
 
-Most Spring Cloud Function apps have a relatively small scope compared to the whole of Spring Boot, so we are able to adapt it to these functional bean definitions easily. If you step outside that limited scope, you can extend your Spring Cloud Function app by switching back to `@Bean` style configuration, or by using a hybrid approach. If you want to take advantage of Spring Boot autoconfiguration for integrations with external datastores, for example, you will need to use `@EnableAutoConfiguration`. Your functions can still be defined using the functional declarations if you want (i.e. the "hybrid" style), but in that case you will need to explicitly switch off the "full functional mode" using `spring.functional.enabled=false` so that Spring Boot can take back control.
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+Most Spring Cloud Function apps have a relatively small scope compared to the whole of Spring Boot, so we are able to adapt it to these functional bean definitions easily. If you step outside that limited scope, you can extend your Spring Cloud Function app by switching back to `@Bean` style configuration, or by using a hybrid approach. If you want to take advantage of Spring Boot autoconfiguration for integrations with external datastores, for example, you will need to use `@EnableAutoConfiguration`. Your functions can still be defined using the functional declarations if you want (i.e. the "hybrid" style), but in that case you will need to explicitly switch off the "full functional mode" using `spring.functional.enabled=false` so that Spring Boot can take back control.