diff --git a/cores/arduino/USB/USBCore.cpp b/cores/arduino/USB/USBCore.cpp
index 8d83b9df6..40f0f45d0 100644
--- a/cores/arduino/USB/USBCore.cpp
+++ b/cores/arduino/USB/USBCore.cpp
@@ -602,6 +602,9 @@ uint8_t USBDeviceClass::armRecv(uint32_t ep)
 	return usbd.epBank0ByteCount(ep);
 }
 
+// Timeout for sends
+#define TX_TIMEOUT_MS 70
+
 // Blocking Send of data to an endpoint
 uint32_t USBDeviceClass::send(uint32_t ep, const void *data, uint32_t len)
 {
@@ -672,9 +675,15 @@ uint32_t USBDeviceClass::send(uint32_t ep, const void *data, uint32_t len)
 		// RAM buffer is full, we can send data (IN)
 		usbd.epBank1SetReady(ep);
 
+		// convert the timeout from microseconds to a number of times through
+		// the wait loop; it takes (roughly) 16 clock cycles per iteration.
+		uint32_t timeout = microsecondsToClockCycles(TX_TIMEOUT_MS * 1000) / 16;
+
 		// Wait for transfer to complete
 		while (!usbd.epBank1IsTransferComplete(ep)) {
-			;  // need fire exit.
+			if (timeout-- == 0) {
+				return -1;
+			}
 		}
 		written += length;
 		len -= length;