diff --git a/htdocs/projet/class/task.class.php b/htdocs/projet/class/task.class.php
index d9ad1111fc7..70f8d998f4b 100644
--- a/htdocs/projet/class/task.class.php
+++ b/htdocs/projet/class/task.class.php
@@ -1724,26 +1724,32 @@ class Task extends CommonObjectLine
 			$ret = -1;
 		}
 
-		if ($ret == 1 && ($this->timespent_old_duration != $this->timespent_duration)) {
-			// Recalculate amount of time spent for task and update denormalized field
-			$sql = "UPDATE ".MAIN_DB_PREFIX."projet_task";
-			$sql .= " SET duration_effective = (SELECT SUM(task_duration) FROM ".MAIN_DB_PREFIX."projet_task_time as ptt where ptt.fk_task = ".((int) $this->id).")";
-			if (isset($this->progress)) {
-				$sql .= ", progress = ".((float) $this->progress); // Do not overwrite value if not provided
-			}
-			$sql .= " WHERE rowid = ".((int) $this->id);
+		if ($ret == 1 && (($this->timespent_old_duration != $this->timespent_duration) || !empty($conf->global->TIMESPENT_ALWAYS_UPDATE_THM))) {
 
-			dol_syslog(get_class($this)."::updateTimeSpent", LOG_DEBUG);
-			if (!$this->db->query($sql)) {
-				$this->error = $this->db->lasterror();
-				$this->db->rollback();
-				$ret = -2;
+			if($this->timespent_old_duration != $this->timespent_duration) {
+				// Recalculate amount of time spent for task and update denormalized field
+				$sql = "UPDATE " . MAIN_DB_PREFIX . "projet_task";
+				$sql .= " SET duration_effective = (SELECT SUM(task_duration) FROM " . MAIN_DB_PREFIX . "projet_task_time as ptt where ptt.fk_task = " . ((int)$this->id) . ")";
+				if (isset($this->progress)) {
+					$sql .= ", progress = " . ((float)$this->progress); // Do not overwrite value if not provided
+				}
+				$sql .= " WHERE rowid = " . ((int)$this->id);
+
+				dol_syslog(get_class($this) . "::updateTimeSpent", LOG_DEBUG);
+				if (!$this->db->query($sql)) {
+					$this->error = $this->db->lasterror();
+					$this->db->rollback();
+					$ret = -2;
+				}
 			}
 
 			// Update hourly rate of this time spent entry, but only if it was not set initialy
 			$sql = "UPDATE ".MAIN_DB_PREFIX."projet_task_time";
 			$sql .= " SET thm = (SELECT thm FROM ".MAIN_DB_PREFIX."user WHERE rowid = ".((int) $this->timespent_fk_user).")"; // set average hour rate of user
-			$sql .= " WHERE (thm IS NULL OR thm = 0) AND rowid = ".((int) $this->timespent_id);
+			$sql .= " WHERE rowid = ".((int) $this->timespent_id);
+			if(empty($conf->global->TIMESPENT_ALWAYS_UPDATE_THM)) { // then if not empty we always update, in case of new thm for user, or change user of task time line
+				$sql .= " AND (thm IS NULL OR thm = 0)";
+			}
 
 			dol_syslog(get_class($this)."::addTimeSpent", LOG_DEBUG);
 			if (!$this->db->query($sql)) {