diff --git a/cmdline/state.c b/cmdline/state.c
index 1fbc564b..06b27d89 100644
--- a/cmdline/state.c
+++ b/cmdline/state.c
@@ -5839,13 +5839,15 @@ static void state_progress_graph(struct snapraid_state* state, struct snapraid_i
 int state_progress(struct snapraid_state* state, struct snapraid_io* io, block_off_t blockpos, block_off_t countpos, block_off_t countmax, data_off_t countsize)
 {
 	time_t now;
+	uint64_t thermal_now;
 	int pred;
 
 	now = time(0);
+	thermal_now = os_tick_sec();
 
 	/* thermal measure */
-	if (now > state->thermal_latest + THERMAL_PERIOD_SECONDS || state->opt.fake_device) {
-		state->thermal_latest = now;
+	if (thermal_now > state->thermal_latest + THERMAL_PERIOD_SECONDS || state->opt.fake_device) {
+		state->thermal_latest = thermal_now;
 		state_thermal(state, now);
 	}
 
diff --git a/cmdline/state.h b/cmdline/state.h
index 368728c8..c97b304d 100644
--- a/cmdline/state.h
+++ b/cmdline/state.h
@@ -161,8 +161,8 @@ struct snapraid_state {
 	int thermal_stop_gathering; /**< If thermal data gathering is stopped */
 	int thermal_ambient_temperature; /**< Ambient themperature. 0 if not available */
 	int thermal_highest_temperature; /**< Current highest temperature */
-	time_t thermal_first; /**< Time of the first measure */
-	time_t thermal_latest; /**< Time of latest measure */
+	uint64_t thermal_first; /**< Monotonic time of the first measure */
+	uint64_t thermal_latest; /**< Monotonic time of latest measure */
 	int thermal_cooldown_time; /**< Cooldown wait time in seconds */
 	int thermal_temperature_limit; /**< Upper limit temperature of the operating range */
 
diff --git a/cmdline/thermal.c b/cmdline/thermal.c
index 5496fd09..a306fc78 100644
--- a/cmdline/thermal.c
+++ b/cmdline/thermal.c
@@ -265,7 +265,7 @@ int state_thermal(struct snapraid_state* state, time_t now)
 
 		/* insert the new data point */
 		found->data[found->count].temperature = temperature;
-		found->data[found->count].time = now - state->thermal_first;
+		found->data[found->count].time = state->thermal_latest - state->thermal_first;
 		++found->count;
 
 		if (state->opt.fake_device) {
@@ -386,8 +386,8 @@ int state_thermal_begin(struct snapraid_state* state, time_t now)
 		return 1;
 
 	/* initial thermal measure */
-	state->thermal_first = now;
-	state->thermal_latest = now;
+	state->thermal_first = os_tick_sec();
+	state->thermal_latest = state->thermal_first;
 	state_thermal(state, now);
 
 	if (state->thermal_ambient_temperature != 0) {