diff --git a/porthole/README.md b/porthole/README.md
index 6cb68f3..8f3976d 100644
--- a/porthole/README.md
+++ b/porthole/README.md
@@ -2,6 +2,8 @@
 `porthole` is a simple application to expose services running on your localhost
 via some other host.
 
+**NOTE**: Currently, only TCP-based services are supported.
+
 ## Quickstart
 To use `porthole`, you need to have the server running on a host that is exposed
 to the WWW.