diff --git a/protocol/wayland.xml b/protocol/wayland.xml
index 784d9712..2ba28438 100644
--- a/protocol/wayland.xml
+++ b/protocol/wayland.xml
@@ -258,6 +258,12 @@
 	for the pool from the file descriptor passed when the pool was
 	created, but using the new size.  This request can only be
 	used to make the pool bigger.
+
+        This request only changes the amount of bytes that are mmapped
+        by the server and does not touch the file corresponding to the
+        file descriptor passed at creation time. It is the client's
+        responsibility to ensure that the file is at least as big as
+        the new pool size.
       </description>
       <arg name="size" type="int" summary="new size of the pool, in bytes"/>
     </request>