diff --git a/include/libdivecomputer/hw_ostc.h b/include/libdivecomputer/hw_ostc.h
index 4dfb523..2b293e2 100644
--- a/include/libdivecomputer/hw_ostc.h
+++ b/include/libdivecomputer/hw_ostc.h
@@ -65,7 +65,7 @@ dc_status_t
 hw_ostc_extract_dives (dc_device_t *device, const unsigned char data[], unsigned int size, dc_dive_callback_t callback, void *userdata);
 
 dc_status_t
-hw_ostc_parser_create (dc_parser_t **parser, dc_context_t *context, unsigned int frog);
+hw_ostc_parser_create (dc_parser_t **parser, dc_context_t *context, unsigned int hwos);
 
 dc_status_t
 hw_ostc_device_fwupdate (dc_device_t *abstract, const char *filename);
diff --git a/include/libdivecomputer/hw_ostc3.h b/include/libdivecomputer/hw_ostc3.h
index c60dc63..56244ed 100644
--- a/include/libdivecomputer/hw_ostc3.h
+++ b/include/libdivecomputer/hw_ostc3.h
@@ -64,6 +64,9 @@ hw_ostc3_device_config_reset (dc_device_t *abstract);
 dc_status_t
 hw_ostc3_device_fwupdate (dc_device_t *abstract, const char *filename);
 
+dc_status_t
+hw_ostc3_parser_create (dc_parser_t **out, dc_context_t *context, unsigned int model);
+
 #ifdef __cplusplus
 }
 #endif /* __cplusplus */
diff --git a/src/hw_ostc3.c b/src/hw_ostc3.c
index 0ed1874..2f88bf0 100644
--- a/src/hw_ostc3.c
+++ b/src/hw_ostc3.c
@@ -595,7 +595,11 @@ hw_ostc3_device_foreach (dc_device_t *abstract, dc_dive_callback_t callback, voi
 
 	// Emit a device info event.
 	dc_event_devinfo_t devinfo;
-	devinfo.firmware = array_uint16_be (id + 2);
+	if (device->hardware == OSTC4) {
+		devinfo.firmware = array_uint16_le (id + 2);
+	} else {
+		devinfo.firmware = array_uint16_be (id + 2);
+	}
 	devinfo.serial = array_uint16_le (id + 0);
 	if (device->hardware != UNKNOWN) {
 		devinfo.model = device->hardware;
diff --git a/src/hw_ostc_parser.c b/src/hw_ostc_parser.c
index b6a6989..7401bc3 100644
--- a/src/hw_ostc_parser.c
+++ b/src/hw_ostc_parser.c
@@ -59,6 +59,8 @@
 #define OSTC3_GAUGE 2
 #define OSTC3_APNEA 3
 
+#define OSTC4      0x3B
+
 typedef struct hw_ostc_sample_info_t {
 	unsigned int type;
 	unsigned int divisor;
@@ -74,6 +76,7 @@ typedef struct hw_ostc_layout_t {
 	unsigned int salinity;
 	unsigned int duration;
 	unsigned int temperature;
+	unsigned int firmware;
 } hw_ostc_layout_t;
 
 typedef struct hw_ostc_gasmix_t {
@@ -83,7 +86,8 @@ typedef struct hw_ostc_gasmix_t {
 
 typedef struct hw_ostc_parser_t {
 	dc_parser_t base;
-	unsigned int frog;
+	unsigned int hwos;
+	unsigned int model;
 	// Cached fields.
 	unsigned int cached;
 	unsigned int version;
@@ -119,6 +123,7 @@ static const hw_ostc_layout_t hw_ostc_layout_ostc = {
 	43, /* salinity */
 	47, /* duration */
 	13, /* temperature */
+	32, /* firmware */
 };
 
 static const hw_ostc_layout_t hw_ostc_layout_frog = {
@@ -130,6 +135,7 @@ static const hw_ostc_layout_t hw_ostc_layout_frog = {
 	43, /* salinity */
 	47, /* duration */
 	19, /* temperature */
+	34, /* firmware */
 };
 
 static const hw_ostc_layout_t hw_ostc_layout_ostc3 = {
@@ -141,6 +147,7 @@ static const hw_ostc_layout_t hw_ostc_layout_ostc3 = {
 	70, /* salinity */
 	75, /* duration */
 	22, /* temperature */
+	48, /* firmware */
 };
 
 static unsigned int
@@ -181,7 +188,7 @@ hw_ostc_parser_cache (hw_ostc_parser_t *parser)
 	}
 
 	// Check the profile version
-	unsigned int version = data[parser->frog ? 8 : 2];
+	unsigned int version = data[parser->hwos ? 8 : 2];
 	const hw_ostc_layout_t *layout = NULL;
 	unsigned int header = 0;
 	switch (version) {
@@ -267,7 +274,7 @@ hw_ostc_parser_cache (hw_ostc_parser_t *parser)
 }
 
 dc_status_t
-hw_ostc_parser_create (dc_parser_t **out, dc_context_t *context, unsigned int frog)
+hw_ostc_parser_create_internal (dc_parser_t **out, dc_context_t *context, unsigned int hwos, unsigned int model)
 {
 	hw_ostc_parser_t *parser = NULL;
 
@@ -282,7 +289,8 @@ hw_ostc_parser_create (dc_parser_t **out, dc_context_t *context, unsigned int fr
 	}
 
 	// Set the default values.
-	parser->frog = frog;
+	parser->hwos = hwos;
+	parser->model = model;
 	parser->cached = 0;
 	parser->version = 0;
 	parser->header = 0;
@@ -301,6 +309,18 @@ hw_ostc_parser_create (dc_parser_t **out, dc_context_t *context, unsigned int fr
 }
 
 
+dc_status_t
+hw_ostc_parser_create (dc_parser_t **out, dc_context_t *context, unsigned int hwos)
+{
+	return hw_ostc_parser_create_internal (out, context, hwos, 0);
+}
+
+dc_status_t
+hw_ostc3_parser_create (dc_parser_t **out, dc_context_t *context, unsigned int model)
+{
+	return hw_ostc_parser_create_internal (out, context, 1, model);
+}
+
 static dc_status_t
 hw_ostc_parser_set_data (dc_parser_t *abstract, const unsigned char *data, unsigned int size)
 {
@@ -589,6 +609,14 @@ hw_ostc_parser_samples_foreach (dc_parser_t *abstract, dc_sample_callback_t call
 		}
 	}
 
+	// Get the firmware version.
+	unsigned int firmware = 0;
+	if (parser->model == OSTC4) {
+		firmware = array_uint16_le (data + layout->firmware);
+	} else {
+		firmware = array_uint16_be (data + layout->firmware);
+	}
+
 	unsigned int time = 0;
 	unsigned int nsamples = 0;
 
@@ -809,6 +837,10 @@ hw_ostc_parser_samples_foreach (dc_parser_t *abstract, dc_sample_callback_t call
 					if (callback) callback (DC_SAMPLE_TEMPERATURE, sample, userdata);
 					break;
 				case 1: // Deco / NDL
+					// Due to a firmware bug, the deco/ndl info is incorrect for
+					// all OSTC4 dives with a firmware older than version 1.0.8.
+					if (parser->model == OSTC4 && firmware < 0x0810)
+						break;
 					if (data[offset]) {
 						sample.deco.type = DC_DECO_DECOSTOP;
 						sample.deco.depth = data[offset];
diff --git a/src/libdivecomputer.symbols b/src/libdivecomputer.symbols
index 8f83c9b..347db27 100644
--- a/src/libdivecomputer.symbols
+++ b/src/libdivecomputer.symbols
@@ -63,6 +63,7 @@ oceanic_vtpro_parser_create2
 oceanic_veo250_parser_create
 oceanic_atom2_parser_create
 hw_ostc_parser_create
+hw_ostc3_parser_create
 cressi_edy_parser_create
 cressi_leonardo_parser_create
 atomics_cobalt_parser_create
diff --git a/src/parser.c b/src/parser.c
index 505270e..bb3eb7a 100644
--- a/src/parser.c
+++ b/src/parser.c
@@ -116,7 +116,7 @@ dc_parser_new_internal (dc_parser_t **out, dc_context_t *context, dc_family_t fa
 		break;
 	case DC_FAMILY_HW_FROG:
 	case DC_FAMILY_HW_OSTC3:
-		rc = hw_ostc_parser_create (&parser, context, 1);
+		rc = hw_ostc3_parser_create (&parser, context, model);
 		break;
 	case DC_FAMILY_CRESSI_EDY:
 	case DC_FAMILY_ZEAGLE_N2ITION3: