diff --git a/drivers/usb/serial/io_edgeport.c b/drivers/usb/serial/io_edgeport.c
index 5737add..4cca0b8 100644
--- a/drivers/usb/serial/io_edgeport.c
+++ b/drivers/usb/serial/io_edgeport.c
@@ -710,7 +710,7 @@ static void edge_interrupt_callback(struct urb *urb)
 		/* grab the txcredits for the ports if available */
 		position = 2;
 		portNumber = 0;
-		while ((position < length) &&
+		while ((position < length - 1) &&
 				(portNumber < edge_serial->serial->num_ports)) {
 			txCredits = data[position] | (data[position+1] << 8);
 			if (txCredits) {