diff --git a/wled00/improv.cpp b/wled00/improv.cpp
index 646201d3..eef8ad82 100644
--- a/wled00/improv.cpp
+++ b/wled00/improv.cpp
@@ -50,6 +50,7 @@ void handleImprovPacket() {
   uint8_t rpcCommandType = 0;
   char rpcData[128];
   rpcData[0] = 0;
+  if (!Serial) return; // WLEDMM avoid reading from unconnected USB-CDC
 
   while (!timeout) {
     if (Serial.available() < 1) {