diff --git a/hardware/arduino/cores/arduino/USBCore.cpp b/hardware/arduino/cores/arduino/USBCore.cpp
index d3e01706567..76ceb01547f 100644
--- a/hardware/arduino/cores/arduino/USBCore.cpp
+++ b/hardware/arduino/cores/arduino/USBCore.cpp
@@ -290,9 +290,12 @@ int USB_Send(u8 ep, const void* d, int len)
 
 		if (n > len)
 			n = len;
-		len -= n;
 		{
 			LockEP lock(ep);
+			// Frame may have been released by the SOF interrupt handler
+			if (!ReadWriteAllowed())
+				continue;
+			len -= n;
 			if (ep & TRANSFER_ZERO)
 			{
 				while (n--)