diff --git a/src/garmin_parser.c b/src/garmin_parser.c
index 7c4cff5..543346b 100644
--- a/src/garmin_parser.c
+++ b/src/garmin_parser.c
@@ -129,7 +129,7 @@ typedef struct garmin_parser_t {
 		unsigned int setpoint_low_cbar, setpoint_high_cbar;
 		unsigned int setpoint_low_switch_depth_mm, setpoint_high_switch_depth_mm;
 		unsigned int setpoint_low_switch_mode, setpoint_high_switch_mode;
-		dc_gasmix_t *current_gasmix;
+		dc_usage_t current_gasmix_usage;
 	} dive;
 
 	// I count nine (!) different GPS fields Hmm.
@@ -239,11 +239,11 @@ static void garmin_event(struct garmin_parser_t *garmin,
 		sample.gasmix = data;
 		garmin->callback(DC_SAMPLE_GASMIX, &sample, garmin->userdata);
 
-		dc_gasmix_t *gasmix = &garmin->cache.GASMIX[data];
-		if (!garmin->dive.current_gasmix || gasmix->usage != garmin->dive.current_gasmix->usage) {
+		dc_usage_t gasmix_usage = garmin->cache.GASMIX[data].usage;
+		if (gasmix_usage != garmin->dive.current_gasmix_usage) {
 			dc_sample_value_t sample2 = {0};
 			sample2.event.type = SAMPLE_EVENT_STRING;
-			if (gasmix->usage == DC_USAGE_DILUENT) {
+			if (gasmix_usage == DC_USAGE_DILUENT) {
 				sample2.event.name = "Switched to closed circuit";
 			} else {
 				sample2.event.name = "Switched to open circuit bailout";
@@ -252,7 +252,7 @@ static void garmin_event(struct garmin_parser_t *garmin,
 
 			garmin->callback(DC_SAMPLE_EVENT, &sample2, garmin->userdata);
 
-			garmin->dive.current_gasmix = gasmix;
+			garmin->dive.current_gasmix_usage = gasmix_usage;
 		}
 
 		return;
@@ -486,19 +486,22 @@ DECLARE_FIELD(ANY, timestamp, UINT32)
 {
 	garmin->record_data.timestamp = data;
 	if (garmin->callback) {
-		dc_sample_value_t sample = {0};
-
 		// Turn the timestamp relative to the beginning of the dive
-		if (data < garmin->dive.time)
+		if (data < garmin->dive.time) {
+			DEBUG(garmin->base.context, "Timestamp before dive start: %d (dive start: %d)", data, garmin->dive.time);
+
 			return;
-		data -= garmin->dive.time;
+		}
+		data -= garmin->dive.time - 1;
 
 		// Did we already do this?
-		if (data < garmin->record_data.time)
+		if (data == garmin->record_data.time)
 			return;
 
+		garmin->record_data.time = data;
+
 		// Now we're ready to actually update the sample times
-		garmin->record_data.time = data+1;
+		dc_sample_value_t sample = {0};
 		sample.time = data * 1000;
 		garmin->callback(DC_SAMPLE_TIME, &sample, garmin->userdata);
 	}
@@ -656,6 +659,7 @@ DECLARE_FIELD(ACTIVITY, event_group, UINT8) { }
 // SPORT
 DECLARE_FIELD(SPORT, sub_sport, ENUM) {
 	garmin->dive.sub_sport = (ENUM) data;
+	garmin->dive.current_gasmix_usage = DC_USAGE_OPEN_CIRCUIT;
 	dc_divemode_t val;
 	switch (data) {
 	case 55: val = DC_DIVEMODE_GAUGE;
@@ -663,7 +667,10 @@ DECLARE_FIELD(SPORT, sub_sport, ENUM) {
 	case 56:
 	case 57: val = DC_DIVEMODE_FREEDIVE;
 		break;
-	case 63: val = DC_DIVEMODE_CCR;
+	case 63:
+		val = DC_DIVEMODE_CCR;
+		garmin->dive.current_gasmix_usage = DC_USAGE_DILUENT;
+
 		break;
 	default: val = DC_DIVEMODE_OC;
 	}
@@ -1337,7 +1344,10 @@ static int traverse_regular(struct garmin_parser_t *garmin,
 		}
 
 		if (field_desc) {
-			field_desc->parse(garmin, base_type, data);
+			if (field_nr == 253 && !msg_desc->maxfield)
+				DEBUG(garmin->base.context, "Ignoring timestamp field for undefined message.");
+			else
+				field_desc->parse(garmin, base_type, data);
 		} else {
 			unknown_field(garmin, data, msg_name, field_nr, base_type, len);
 		}
@@ -1521,7 +1531,12 @@ traverse_data(struct garmin_parser_t *garmin)
 			// Compressed records are like normal records
 			// with that added relative timestamp
 			DEBUG(garmin->base.context, "Compressed record for type %d", type);
-			parse_ANY_timestamp(garmin, time);
+
+			if (!(garmin->type_desc + type)->msg_desc->maxfield)
+				DEBUG(garmin->base.context, "Ignoring timestamp field for undefined message.");
+			else
+				parse_ANY_timestamp(garmin, time);
+
 			len = traverse_regular(garmin, data, datasize, type, &time);
 		} else if (record & 0x40) {	// Definition record?
 			len = traverse_definition(garmin, data, datasize, record);