diff --git a/src/reefnet_sensus_parser.c b/src/reefnet_sensus_parser.c
index 50fd69e..35fb952 100644
--- a/src/reefnet_sensus_parser.c
+++ b/src/reefnet_sensus_parser.c
@@ -133,7 +133,12 @@ reefnet_sensus_parser_get_datetime (dc_parser_t *abstract, dc_datetime_t *dateti
 
 	unsigned int timestamp = array_uint32_le (abstract->data + 2);
 
-	dc_ticks_t ticks = parser->systime - (parser->devtime - timestamp);
+	dc_ticks_t ticks = parser->systime;
+	if (timestamp < parser->devtime) {
+		ticks -= parser->devtime - timestamp;
+	} else {
+		ticks += timestamp - parser->devtime;
+	}
 
 	if (!dc_datetime_localtime (datetime, ticks))
 		return DC_STATUS_DATAFORMAT;
diff --git a/src/reefnet_sensuspro_parser.c b/src/reefnet_sensuspro_parser.c
index 7e68a72..c303ee9 100644
--- a/src/reefnet_sensuspro_parser.c
+++ b/src/reefnet_sensuspro_parser.c
@@ -132,7 +132,12 @@ reefnet_sensuspro_parser_get_datetime (dc_parser_t *abstract, dc_datetime_t *dat
 
 	unsigned int timestamp = array_uint32_le (abstract->data + 6);
 
-	dc_ticks_t ticks = parser->systime - (parser->devtime - timestamp);
+	dc_ticks_t ticks = parser->systime;
+	if (timestamp < parser->devtime) {
+		ticks -= parser->devtime - timestamp;
+	} else {
+		ticks += timestamp - parser->devtime;
+	}
 
 	if (!dc_datetime_localtime (datetime, ticks))
 		return DC_STATUS_DATAFORMAT;
diff --git a/src/reefnet_sensusultra_parser.c b/src/reefnet_sensusultra_parser.c
index 8aaacca..bad5450 100644
--- a/src/reefnet_sensusultra_parser.c
+++ b/src/reefnet_sensusultra_parser.c
@@ -132,7 +132,12 @@ reefnet_sensusultra_parser_get_datetime (dc_parser_t *abstract, dc_datetime_t *d
 
 	unsigned int timestamp = array_uint32_le (abstract->data + 4);
 
-	dc_ticks_t ticks = parser->systime - (parser->devtime - timestamp);
+	dc_ticks_t ticks = parser->systime;
+	if (timestamp < parser->devtime) {
+		ticks -= parser->devtime - timestamp;
+	} else {
+		ticks += timestamp - parser->devtime;
+	}
 
 	if (!dc_datetime_localtime (datetime, ticks))
 		return DC_STATUS_DATAFORMAT;
diff --git a/src/uwatec_memomouse_parser.c b/src/uwatec_memomouse_parser.c
index f36dc6c..386e984 100644
--- a/src/uwatec_memomouse_parser.c
+++ b/src/uwatec_memomouse_parser.c
@@ -96,7 +96,12 @@ uwatec_memomouse_parser_get_datetime (dc_parser_t *abstract, dc_datetime_t *date
 
 	unsigned int timestamp = array_uint32_le (abstract->data + 11);
 
-	dc_ticks_t ticks = parser->systime - (parser->devtime - timestamp) / 2;
+	dc_ticks_t ticks = parser->systime;
+	if (timestamp < parser->devtime) {
+		ticks -= (parser->devtime - timestamp) / 2;
+	} else {
+		ticks += (timestamp - parser->devtime) / 2;
+	}
 
 	if (!dc_datetime_localtime (datetime, ticks))
 		return DC_STATUS_DATAFORMAT;