diff --git a/cores/arduino/USB/USBCore.cpp b/cores/arduino/USB/USBCore.cpp
index 6f983c0ab..b13ba03e2 100644
--- a/cores/arduino/USB/USBCore.cpp
+++ b/cores/arduino/USB/USBCore.cpp
@@ -177,6 +177,15 @@ uint32_t USBDeviceClass::sendConfiguration(uint32_t maxlen)
 	return true;
 }
 
+static void utox8(uint32_t val, char* s) {
+	for (int i = 0; i < 8; i++) {
+		int d = val & 0XF;
+		val = (val >> 4);
+
+		s[7 - i] = d > 9 ? 'A' + d - 10 : '0' + d;
+	}
+}
+
 bool USBDeviceClass::sendDescriptor(USBSetup &setup)
 {
 	uint8_t t = setup.wValueH;
@@ -221,8 +230,19 @@ bool USBDeviceClass::sendDescriptor(USBSetup &setup)
 		}
 		else if (setup.wValueL == ISERIAL) {
 #ifdef PLUGGABLE_USB_ENABLED
+			// from section 9.3.3 of the datasheet
+			#define SERIAL_NUMBER_WORD_0	*(volatile uint32_t*)(0x0080A00C)
+			#define SERIAL_NUMBER_WORD_1	*(volatile uint32_t*)(0x0080A040)
+			#define SERIAL_NUMBER_WORD_2	*(volatile uint32_t*)(0x0080A044)
+			#define SERIAL_NUMBER_WORD_3	*(volatile uint32_t*)(0x0080A048)
+
 			char name[ISERIAL_MAX_LEN];
-			PluggableUSB().getShortName(name);
+			utox8(SERIAL_NUMBER_WORD_0, &name[0]);
+			utox8(SERIAL_NUMBER_WORD_1, &name[8]);
+			utox8(SERIAL_NUMBER_WORD_2, &name[16]);
+			utox8(SERIAL_NUMBER_WORD_3, &name[24]);
+
+			PluggableUSB().getShortName(&name[32]);
 			return sendStringDescriptor((uint8_t*)name, setup.wLength);
 #endif
 		}
diff --git a/cores/arduino/USB/USBDesc.h b/cores/arduino/USB/USBDesc.h
index 6088ee089..9ea6abcc1 100644
--- a/cores/arduino/USB/USBDesc.h
+++ b/cores/arduino/USB/USBDesc.h
@@ -41,7 +41,7 @@
 #define CDC_TX CDC_ENDPOINT_IN
 #endif
 
-#define ISERIAL_MAX_LEN        33
+#define ISERIAL_MAX_LEN        65
 
 // Defined string description
 #define IMANUFACTURER	1