diff --git a/hardware/arduino/sam/cores/sam/USB/USBCore.cpp b/hardware/arduino/sam/cores/sam/USB/USBCore.cpp
index 711ff8a5d..4ba52631b 100644
--- a/hardware/arduino/sam/cores/sam/USB/USBCore.cpp
+++ b/hardware/arduino/sam/cores/sam/USB/USBCore.cpp
@@ -425,17 +425,15 @@ static void USB_ISR(void)
 		uint8_t requestType = setup.bmRequestType;
 		if (requestType & REQUEST_DEVICETOHOST)
 		{
-			TRACE_CORE(printf(">>> EP0 Int: IN Request\r\n");)
+			TRACE_CORE(puts(">>> EP0 Int: IN Request\r\n");)
 			UDD_WaitIN();
 		}
 		else
 		{
-			TRACE_CORE(printf(">>> EP0 Int: OUT Request\r\n");)
+			TRACE_CORE(puts(">>> EP0 Int: OUT Request\r\n");)
 			UDD_ClearIN();
 		}
 
-
-
 		bool ok = true ;
 		if (REQUEST_STANDARD == (requestType & REQUEST_TYPE))
 		{
@@ -507,6 +505,9 @@ static void USB_ISR(void)
 		else
 		{
 			TRACE_CORE(puts(">>> EP0 Int: ClassInterfaceRequest\r\n");)
+
+			UDD_WaitIN(); // Workaround: need tempo here, else CDC serial won't open correctly
+
 			USBD_InitControl(setup.wLength); // Max length of transfer
 			ok = USBD_ClassInterfaceRequest(setup);
 		}
diff --git a/hardware/arduino/sam/cores/sam/libsam_sam3x8e_gcc_dbg.a b/hardware/arduino/sam/cores/sam/libsam_sam3x8e_gcc_dbg.a
index e59285c72..88d9d7bea 100644
Binary files a/hardware/arduino/sam/cores/sam/libsam_sam3x8e_gcc_dbg.a and b/hardware/arduino/sam/cores/sam/libsam_sam3x8e_gcc_dbg.a differ
diff --git a/hardware/arduino/sam/variants/arduino_due_x/libsam_sam3x8e_gcc_rel.a b/hardware/arduino/sam/variants/arduino_due_x/libsam_sam3x8e_gcc_rel.a
index ab3148aeb..4a27d212b 100644
Binary files a/hardware/arduino/sam/variants/arduino_due_x/libsam_sam3x8e_gcc_rel.a and b/hardware/arduino/sam/variants/arduino_due_x/libsam_sam3x8e_gcc_rel.a differ