diff --git a/cmd_parser.c b/cmd_parser.c
index e7daa9e8..e16fa108 100644
--- a/cmd_parser.c
+++ b/cmd_parser.c
@@ -846,9 +846,14 @@ void parse_mirror(void)
 	if (cmd_words_len < 2)
 		goto err;
 
+	// The first argument is the mirroring (monitor) port
+	uint8_t ret = cmd_parse_port(cmd_words_b[1]);
+	if (ret == 0)
+		goto err;
+	mirroring_port = atoi_results_u8;
+
 	uint8_t w = 2;
 	uint8_t port;
-	uint8_t ret;
 	while (w < cmd_words_len) {
 		uint8_t idx = cmd_words_b[w++];
 		ret = cmd_parse_port(idx);
@@ -858,10 +863,6 @@ void parse_mirror(void)
 		idx += ret;
 		port = atoi_results_u8;
 
-		// Use the first port argument as mirroring_port
-		if (w == 2)
-			mirroring_port = port;
-
 		ret = cmd_buffer[idx];
 		uint16_t pmask = ((uint16_t)1) << port;
 		if (ret != 't')