diff --git a/common/Cargo.toml b/common/Cargo.toml
index d7a7bc0a..8ca71f6b 100644
--- a/common/Cargo.toml
+++ b/common/Cargo.toml
@@ -21,5 +21,4 @@ slog-term.workspace = true
 slog-async.workspace = true
 smf.workspace = true
 thiserror.workspace = true
-tokio.workspace = true
-
+tokio = { workspace = true, features = [ "full" ] }
diff --git a/common/src/ports.rs b/common/src/ports.rs
index 2d7fccf6..cc2d78ef 100644
--- a/common/src/ports.rs
+++ b/common/src/ports.rs
@@ -92,7 +92,13 @@ macro_rules! make_port_type {
                 if s.len() <= $prefix.len() {
                     return Err("Invalid port kind");
                 }
-                let (head, tail) = s.split_at($prefix.len());
+                if !s.is_ascii() {
+                    return Err("Port IDs must be ASCII");
+                }
+                let Some((head, tail)) = s.split_at_checked($prefix.len())
+                else {
+                    return Err("Invalid port kind");
+                };
                 if head.eq_ignore_ascii_case($prefix) {
                     tail.parse::<u8>()
                         .map_err(|_| "Invalid port index")
@@ -606,3 +612,15 @@ pub struct XcvrSettings {
     /// Equalization settings
     pub tx_eq: Option<TxEq>,
 }
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn port_ids_are_ascii() {
+        let e = PortId::try_from("abč0")
+            .expect_err("Should have returned an error");
+        assert_eq!(e.to_string(), "Invalid switch port ID");
+    }
+}