diff --git a/work/meshai/transport/meshcore_transport.py b/work/meshai/transport/meshcore_transport.py
index 8d556f1..0ea7027 100644
--- a/work/meshai/transport/meshcore_transport.py
+++ b/work/meshai/transport/meshcore_transport.py
@@ -206,14 +206,20 @@ class MeshCoreTransport(MeshTransport):
             logger.error("MeshCoreTransport: cannot send, not connected")
             return False
 
-        chan_idx = channel or getattr(self.config, "meshcore_channel_index", 0)
-
         try:
             if destination:
                 result = self._run_coro(
                     self._mc.commands.send_msg(destination, text)
                 )
             else:
+                # Channel-index semantics do NOT cross transports: the passed
+                # `channel` carries Meshtastic channel-index semantics (e.g.
+                # index 8) that have no relationship to MeshCore's separate
+                # channel table. The configured MeshCore channel is therefore
+                # authoritative for broadcasts, so we ignore `channel` here
+                # (this also avoids an explicit channel=0 being treated as
+                # falsy).
+                chan_idx = getattr(self.config, "meshcore_channel_index", 0)
                 result = self._run_coro(
                     self._mc.commands.send_chan_msg(chan_idx, text)
                 )
diff --git a/work/tests/test_meshcore_transport.py b/work/tests/test_meshcore_transport.py
index 5a2b301..0f3eb48 100644
--- a/work/tests/test_meshcore_transport.py
+++ b/work/tests/test_meshcore_transport.py
@@ -202,8 +202,9 @@ class TestSendMessageChannel:
         # _mc is None, no loop started
         assert t.send_message("test") is False
 
-    def test_uses_config_channel_index_when_channel_zero(self):
-        cfg = _mc_config(meshcore_channel_index=3)
+    def _transport_with_configured_index(self, index):
+        """Build a MeshCoreTransport whose config sets meshcore_channel_index."""
+        cfg = _mc_config(meshcore_channel_index=index)
         t = MeshCoreTransport(cfg)
         ok = MagicMock()
         ok.is_error.return_value = False
@@ -217,9 +218,32 @@ class TestSendMessageChannel:
         thread = threading.Thread(target=loop.run_forever, daemon=True)
         thread.start()
         t._loop_thread = thread
+        return t, mc
+
+    def test_uses_config_channel_index_when_channel_zero(self):
+        t, mc = self._transport_with_configured_index(3)
         try:
             t.send_message("hi", channel=0)
-            # channel=0 is falsy → falls back to meshcore_channel_index=3
+            # channel=0 must not be treated as falsy-fallthrough: broadcasts
+            # always use the configured meshcore_channel_index=3.
+            mc.commands.send_chan_msg.assert_awaited_once_with(3, "hi")
+        finally:
+            _cleanup(t)
+
+    def test_uses_config_channel_index_when_channel_default(self):
+        t, mc = self._transport_with_configured_index(3)
+        try:
+            t.send_message("hi")  # default channel param
+            mc.commands.send_chan_msg.assert_awaited_once_with(3, "hi")
+        finally:
+            _cleanup(t)
+
+    def test_ignores_meshtastic_channel_index(self):
+        # channel=8 carries Meshtastic channel-index semantics that do NOT map
+        # to MeshCore's channel table; the configured index (3) is authoritative.
+        t, mc = self._transport_with_configured_index(3)
+        try:
+            t.send_message("hi", channel=8)
             mc.commands.send_chan_msg.assert_awaited_once_with(3, "hi")
         finally:
             _cleanup(t)