diff --git a/tests/scripts/thread-cert/simulator.py b/tests/scripts/thread-cert/simulator.py
index 960b3553e..a54cbf274 100755
--- a/tests/scripts/thread-cert/simulator.py
+++ b/tests/scripts/thread-cert/simulator.py
@@ -528,7 +528,8 @@ class VirtualTime(BaseSimulator):
 
         if len(event) == 5:
             event_time, sequence, port, type, datalen = event
-            dbg_print("Pop event: ", event_time, port, type, datalen)
+            data = b''
+            dbg_print("Pop event: ", event_time, port, type, datalen, "(no data)")
         else:
             event_time, sequence, port, type, datalen, data = event
             dbg_print(
@@ -562,6 +563,10 @@ class VirtualTime(BaseSimulator):
         elif type == self.OT_SIM_EVENT_UART_WRITE:
             message += data
             self._send_message(message, port)
+        else:
+            raise NotImplementedError(f'Unknown event type: {type}')
+
+        self.awake_devices.add(port)
 
     def sync_devices(self):
         self.current_time = self._pause_time