diff --git a/crates/collab-net/src/invite.rs b/crates/collab-net/src/invite.rs
index 617ad518..47ca1850 100644
--- a/crates/collab-net/src/invite.rs
+++ b/crates/collab-net/src/invite.rs
@@ -220,7 +220,8 @@ fn valid_host(s: &str) -> bool {
         return true;
     }
     let Some((name, port)) = s.rsplit_once(':') else { return false };
-    port.parse::<u16>().is_ok_and(|p| p != 0)
+    port.bytes().all(|b| b.is_ascii_digit())
+        && port.parse::<u16>().is_ok_and(|p| p != 0)
         && (1..=253).contains(&name.len())
         && name.bytes().all(|b| b.is_ascii_alphanumeric() || b == b'-' || b == b'.')
         && !name.starts_with(['-', '.'])
diff --git a/crates/collab-net/src/invite_tests.rs b/crates/collab-net/src/invite_tests.rs
index 02017517..d4d13296 100644
--- a/crates/collab-net/src/invite_tests.rs
+++ b/crates/collab-net/src/invite_tests.rs
@@ -123,3 +123,11 @@ proptest! {
         prop_assert_eq!(Invite::parse(&i.url()), Ok(i));
     }
 }
+
+#[test]
+fn port_must_be_all_digits() {
+    assert!(Endpoint::parse("ws://localhost:80/").is_ok());
+    for bad in ["ws://localhost:+80/", "ws://localhost:-80/", "ws://localhost:/"] {
+        assert!(Endpoint::parse(bad).is_err(), "accepted {bad}");
+    }
+}