diff --git a/cores/esp32/USB.cpp b/cores/esp32/USB.cpp
index a1fe50944db..6174f28d738 100644
--- a/cores/esp32/USB.cpp
+++ b/cores/esp32/USB.cpp
@@ -165,7 +165,7 @@ bool ESPUSB::begin(){
             StreamString s;
             uint8_t m[6];
             esp_efuse_mac_get_default(m);
-            s.printf("%02X:%02X:%02X:%02X:%02X:%02X", m[0], m[1], m[2], m[3], m[4], m[5]);
+            s.printf("%02X%02X%02X%02X%02X%02X", m[0], m[1], m[2], m[3], m[4], m[5]);
             serial_number = s;
         }
 #endif