diff --git a/hardware/serial-dmm/protocol.c b/hardware/serial-dmm/protocol.c
index 6ca5e73e..fab6c4ae 100644
--- a/hardware/serial-dmm/protocol.c
+++ b/hardware/serial-dmm/protocol.c
@@ -80,7 +80,9 @@ static void handle_new_data(struct sr_dev_inst *sdi, int dmm, void *info)
 	/* Try to get as much data as the buffer can hold. */
 	len = DMM_BUFSIZE - devc->buflen;
 	len = serial_read(serial, devc->buf + devc->buflen, len);
-	if (len < 1) {
+	if (len == 0)
+		return; /* No new bytes, nothing to do. */
+	if (len < 0) {
 		sr_err("Serial port read error: %d.", len);
 		return;
 	}