diff --git a/src/amps/amps.c b/src/amps/amps.c
index d2dd948..8420d05 100644
--- a/src/amps/amps.c
+++ b/src/amps/amps.c
@@ -704,7 +704,7 @@ void amps_rx_signaling_tone(amps_t *amps, int tone, double quality)
 	case TRANS_CALL:
 		if (!tone)
 			break;
-		/* fall through */
+		/* FALLTHRU */
 	case TRANS_CALL_RELEASE:
 	case TRANS_CALL_RELEASE_SEND:
 		/* also loosing singaling tone indicates release confirm (after alerting) */
diff --git a/src/amps/dsp.c b/src/amps/dsp.c
index 93f4eab..8c3409a 100644
--- a/src/amps/dsp.c
+++ b/src/amps/dsp.c
@@ -553,6 +553,7 @@ static void fsk_rx_bit(amps_t *amps, sample_t *spl, int len, int pos, int begin,
 		case 0x01:
 			if (!amps->fsk_rx_sync_tolerant)
 				break;
+			/* FALLTHRU */
 		case 0x00:
 #ifdef DEBUG_DECODER
 			printf("Sync word detected (positive)\n");
@@ -568,6 +569,7 @@ prepare_frame:
 		case 0x81:
 			if (!amps->fsk_rx_sync_tolerant)
 				break;
+			/* FALLTHRU */
 		case 0x80:
 #ifdef DEBUG_DECODER
 			printf("Sync word detected (negative)\n");
diff --git a/src/anetz/dsp.c b/src/anetz/dsp.c
index 3bcf112..2d58702 100644
--- a/src/anetz/dsp.c
+++ b/src/anetz/dsp.c
@@ -196,7 +196,7 @@ void sender_receive(sender_t *sender, sample_t *samples, int length, double rf_l
 	switch (squelch(&anetz->squelch, rf_level_db, (double)length / (double)anetz->sender.samplerate)) {
 	case SQUELCH_LOSS:
 		anetz_loss_indication(anetz, LOSS_TIME);
-		// fall through:
+		/* FALLTHRU */
 	case SQUELCH_MUTE:
 		memset(samples, 0, sizeof(*samples) * length);
 		break;
diff --git a/src/bnetz/dsp.c b/src/bnetz/dsp.c
index 6915d9f..0c060fc 100644
--- a/src/bnetz/dsp.c
+++ b/src/bnetz/dsp.c
@@ -219,7 +219,7 @@ void sender_receive(sender_t *sender, sample_t *samples, int length, double rf_l
 	switch (squelch(&bnetz->squelch, rf_level_db, (double)length / (double)bnetz->sender.samplerate)) {
 	case SQUELCH_LOSS:
 		bnetz_loss_indication(bnetz, LOSS_TIME);
-		// fall through:
+		/* FALLTHRU */
 	case SQUELCH_MUTE:
 		memset(samples, 0, sizeof(*samples) * length);
 		break;
diff --git a/src/cnetz/fsk_demod.c b/src/cnetz/fsk_demod.c
index 5acf8b5..54ad41f 100644
--- a/src/cnetz/fsk_demod.c
+++ b/src/cnetz/fsk_demod.c
@@ -379,7 +379,7 @@ got_sync:
 		break;
 	case FSK_SYNC_NEGATIVE:
 		bit = 1 - bit;
-		/* fall through */
+		/* FALLTHRU */
 	case FSK_SYNC_POSITIVE:
 		fsk->rx_buffer[fsk->rx_buffer_count] = bit + '0';
 		if (++fsk->rx_buffer_count == 150) {
diff --git a/src/cnetz/telegramm.c b/src/cnetz/telegramm.c
index eddaa01..72f0228 100644
--- a/src/cnetz/telegramm.c
+++ b/src/cnetz/telegramm.c
@@ -454,7 +454,7 @@ int init_telegramm(void)
 
 const char *telegramm2rufnummer(telegramm_t *telegramm)
 {
-	static char rufnummer[9];
+	static char rufnummer[32]; /* make GCC happy (overflow check) */
 
 	sprintf(rufnummer, "%d%d%05d", telegramm->futln_nationalitaet, telegramm->futln_heimat_fuvst_nr, telegramm->futln_rest_nr);
 
diff --git a/src/cnetz/transaction.c b/src/cnetz/transaction.c
index 29e5df4..8184aac 100644
--- a/src/cnetz/transaction.c
+++ b/src/cnetz/transaction.c
@@ -30,7 +30,7 @@
 
 const char *transaction2rufnummer(transaction_t *trans)
 {
-	static char rufnummer[9];
+	static char rufnummer[32]; /* make GCC happy (overflow check) */
 
 	sprintf(rufnummer, "%d%d%05d", trans->futln_nat, trans->futln_fuvst, trans->futln_rest);
 
diff --git a/src/jolly/dsp.c b/src/jolly/dsp.c
index fff5390..00407eb 100644
--- a/src/jolly/dsp.c
+++ b/src/jolly/dsp.c
@@ -384,7 +384,8 @@ void sender_send(sender_t *sender, sample_t *samples, uint8_t *power, int length
 				memset(samples + count, 0, sizeof(*samples) * (length - count));
 			break;
 		}
-		/* fall through, in case of no voice */
+		/* in case of no voice: */
+		/* FALLTHRU */
 	default:
 		memset(power, 1, length);
 		dial_tone(jolly, samples, length);
diff --git a/src/libsound/sound_alsa.c b/src/libsound/sound_alsa.c
index 5c75fa4..c62b7c9 100644
--- a/src/libsound/sound_alsa.c
+++ b/src/libsound/sound_alsa.c
@@ -239,7 +239,7 @@ static void gen_paging_tone(sound_t *sound, int16_t *samples, int length, enum p
 	case PAGING_SIGNAL_NOTONE:
 		/* no tone if paging signal is on */
 		on = !on;
-		// fall through
+		/* FALLTHRU */
 	case PAGING_SIGNAL_TONE:
 		/* tone if paging signal is on */
 		if (on) {
@@ -261,7 +261,7 @@ static void gen_paging_tone(sound_t *sound, int16_t *samples, int length, enum p
 	case PAGING_SIGNAL_NEGATIVE:
 		/* negative signal if paging signal is on */
 		on = !on;
-		// fall through
+		/* FALLTHRU */
 	case PAGING_SIGNAL_POSITIVE:
 		/* positive signal if paging signal is on */
 		if (on)