diff --git a/helper/dashtouch_helper/daemon.py b/helper/dashtouch_helper/daemon.py
index e665a9f..c705663 100644
--- a/helper/dashtouch_helper/daemon.py
+++ b/helper/dashtouch_helper/daemon.py
@@ -65,7 +65,10 @@ def __init__(self, serial_number: str, port: str | None = None):
                       # Mirrors the firmware's transient PAUSE state (see
                       # docs/protocol.md). Updated from PAUSE_OK replies and
                       # STATUS_OK's paused= field; never persisted.
-                      "paused": False}
+                      "paused": False,
+                      # Why the board can't be picked out, while that's the
+                      # case (currently: several usbmodem ports at once).
+                      "port_problem": None}
 
     # -- connection lifecycle -----------------------------------------------
     def _on_connect(self) -> None:
@@ -297,7 +300,9 @@ def health(self) -> list[dict]:
             "label": "Device",
             "ok": connected,
             "state": "ok" if connected else "bad",
-            "detail": "Connected" if connected else "Not connected",
+            "detail": "Connected" if connected
+                      else "More than one board is plugged in" if self.state["port_problem"]
+                      else "Not connected",
             "fix": "help-not-connected",
         })
 
@@ -396,7 +401,21 @@ def run_forever(self) -> None:
             print(f"web UI: {origin}")
             print(f"(the full link, with your session token, is in {webui.URL_PATH})")
         while True:
-            port = self.port or serial_link.find_port()
+            try:
+                port = self.port or serial_link.find_port()
+            except serial_link.AmbiguousPortError as e:
+                # Letting this escape crash-looped the helper under
+                # launchd's KeepAlive until someone unplugged a board. Wait
+                # it out like any other absence, and say why once rather
+                # than every second.
+                if self.state["port_problem"] != str(e):
+                    msg = f"{e} — unplug the one that isn't Dashboard Touch"
+                    print(msg, file=sys.stderr)
+                    self.log_event("helper", msg)
+                self.state["port_problem"] = str(e)
+                port = None
+            else:
+                self.state["port_problem"] = None
             if port is None:
                 self.state["connected"] = False
                 time.sleep(1.0)
diff --git a/helper/tests/test_daemon.py b/helper/tests/test_daemon.py
index 53e18ce..25e354a 100644
--- a/helper/tests/test_daemon.py
+++ b/helper/tests/test_daemon.py
@@ -752,3 +752,46 @@ def test_health_picks_up_a_repaired_keychain_without_a_restart():
         rows = {r["id"]: r for r in d.health()}
     assert rows["pairing"]["state"] == "ok"
     assert rows["password"]["state"] == "ok"
+
+
+def test_run_forever_waits_out_several_boards_instead_of_crashing(monkeypatch, capsys):
+    # With two usbmodem ports, find_port() raised straight out of
+    # run_forever: under launchd's KeepAlive, a crash-loop until a board was
+    # unplugged. The helper must keep looking, and connect once it can.
+    d = make_daemon()
+    monkeypatch.setattr(daemon.webui, "start", lambda self: "http://127.0.0.1:3274/?token=T")
+    found = iter([daemon.serial_link.AmbiguousPortError("several boards found: [a, b]")] * 3
+                 + ["/dev/fake"])
+
+    def find_port():
+        r = next(found)
+        if isinstance(r, Exception):
+            raise r
+        return r
+
+    monkeypatch.setattr(daemon.serial_link, "find_port", find_port)
+    monkeypatch.setattr(daemon.time, "sleep", lambda s: None)
+    opened = []
+    monkeypatch.setattr(daemon.serial_link, "open_port",
+                        lambda port: opened.append(port) or mock.Mock())
+
+    def stop(ser):
+        raise RuntimeError("stop test loop")
+
+    monkeypatch.setattr(daemon.serial_link, "read_line", stop)
+    with pytest.raises(RuntimeError, match="stop test loop"):
+        d.run_forever()
+    assert opened == ["/dev/fake"]
+    assert d.state["port_problem"] is None
+    # Said once, not once per retry.
+    said = [e for e in d.events if "several boards found" in e["text"]]
+    assert len(said) == 1
+    assert capsys.readouterr().err.count("several boards found") == 1
+
+
+def test_health_says_when_several_boards_are_the_reason():
+    d = make_daemon()
+    d.state["port_problem"] = "several boards found: [a, b]"
+    rows = {r["id"]: r for r in d.health()}
+    assert rows["device"]["state"] == "bad"
+    assert rows["device"]["detail"] == "More than one board is plugged in"