diff --git a/docs/about/emulation.rst b/docs/about/emulation.rst
index 0ad0b86f0d..a2eefe3f3f 100644
--- a/docs/about/emulation.rst
+++ b/docs/about/emulation.rst
@@ -129,8 +129,9 @@ causing most hypervisors to trap and fault on them.
 .. warning::
    Semihosting inherently bypasses any isolation there may be between
    the guest and the host. As a result a program using semihosting can
-   happily trash your host system. You should only ever run trusted
-   code with semihosting enabled.
+   happily trash your host system. Some semihosting calls (e.g.
+   ``SYS_READC``) can block execution indefinitely. You should only
+   ever run trusted code with semihosting enabled.
 
 Redirection
 ~~~~~~~~~~~