diff --git a/src/auracast/multicast_server.py b/src/auracast/multicast_server.py
index 32e4b98..f98273a 100644
--- a/src/auracast/multicast_server.py
+++ b/src/auracast/multicast_server.py
@@ -26,6 +26,11 @@ async def initialize(conf: auracast_config.AuracastConfigGroup):
                     log.info('Using: %s', device)
                     conf.transport = f'serial:{device},115200,rtscts'
                     break
+
+        # check again if transport is still auto
+        if conf.transport == 'auto':
+            HTTPException(status_code=500, detail='No suitable transport found.')
+
         # initialize the streams dict
         global_config_group = conf
         log.info(