diff --git a/src/crosvm/sys/unix/cmdline.rs b/src/crosvm/sys/unix/cmdline.rs
index d5fcd99fc8..5d4b45e246 100644
--- a/src/crosvm/sys/unix/cmdline.rs
+++ b/src/crosvm/sys/unix/cmdline.rs
@@ -59,10 +59,31 @@ pub struct DevicesCommand {
 
     #[argh(
         option,
-        arg_name = "serial options",
+        arg_name = "vhost=PATH,type=TYPE,[hardware=HW,num=NUM,path=PATH,input=PATH,console,earlycon,stdin]",
         from_str_fn(parse_vu_serial_options)
     )]
-    /// start a serial device (see help from run command for options)
+    /// comma separated key=value pairs for setting up serial
+    /// devices. Can be given more than once.
+    /// Possible key values:
+    ///     vhost=PATH - Path to a vhost-user endpoint to listen to.
+    ///     type=(stdout,syslog,sink,file) - Where to route the
+    ///        serial device
+    ///     hardware=(serial,virtio-console) - Which type of serial
+    ///        hardware to emulate. Defaults to 8250 UART (serial).
+    ///     num=(1,2,3,4) - Serial Device Number. If not provided,
+    ///        num will default to 1.
+    ///     path=PATH - The path to the file to write to when
+    ///        type=file
+    ///     input=PATH - The path to the file to read from when not
+    ///        stdin
+    ///     console - Use this serial device as the guest console.
+    ///        Can only be given once. Will default to first
+    ///        serial port if not provided.
+    ///     earlycon - Use this serial device as the early console.
+    ///        Can only be given once.
+    ///     stdin - Direct standard input to this serial device.
+    ///        Can only be given once. Will default to first serial
+    ///        port if not provided.
     pub serial: Vec<VhostUserParams<SerialParameters>>,
 
     #[argh(option, arg_name = "block options")]