diff --git a/src/rtl_fm.c b/src/rtl_fm.c
index 037793c..f2542cb 100644
--- a/src/rtl_fm.c
+++ b/src/rtl_fm.c
@@ -193,7 +193,7 @@ void usage(void)
 		"\t    raw mode outputs 2x16 bit IQ pairs\n"
 		"\t[-s sample_rate (default: 24k)]\n"
 		"\t[-d device_index (default: 0)]\n"
-		"\t[-T enable bias-T on GPIO PIN 0 (works for rtl-sdr.com v3 dongles)]\n"
+		"\t[-T enable bias-T on GPIO PIN 0 (works for rtl-sdr.com v3/v4 dongles)]\n"
 		"\t[-g tuner_gain (default: automatic)]\n"
 		"\t[-l squelch_level (default: 0/off)]\n"
 		//"\t    for fm squelch is inverted\n"