diff --git a/ftdi-gpio.c b/ftdi-gpio.c
index dca9488..b49e267 100644
--- a/ftdi-gpio.c
+++ b/ftdi-gpio.c
@@ -102,7 +102,7 @@ static void ftdi_gpio_parse_config(struct ftdi_gpio *ftdi_gpio, char *control_de
 	// Interface
 	interface = c + 1;
 	if (*interface != 'A' &&
-	    *interface != 'A' &&
+	    *interface != 'B' &&
 	    *interface != 'C' &&
 	    *interface != 'D') {
 		errx(1, "Invalid interface '%c'", *interface);