diff --git a/htdocs/langs/en_US/projects.lang b/htdocs/langs/en_US/projects.lang
index 279bf99d162..3fbcbb0dca7 100644
--- a/htdocs/langs/en_US/projects.lang
+++ b/htdocs/langs/en_US/projects.lang
@@ -269,3 +269,5 @@ OneLinePerPeriod=One line per period
 RefTaskParent=Ref. Parent Task
 ProfitIsCalculatedWith=Profit is calculated using
 AddPersonToTask=Add also to tasks
+PROJECT_CLASSIFY_CLOSED_WHEN_ALL_TASKS_DONE=Classify project as closed when all its tasks are completed (100%% progress)
+PROJECT_CLASSIFY_CLOSED_WHEN_ALL_TASKS_DONE_help=Note: existing projects with all tasks at 100 %% progress won't be affected: you will have to close them manually. This option only affects open projects.
diff --git a/htdocs/langs/fr_FR/projects.lang b/htdocs/langs/fr_FR/projects.lang
index 1affdad0889..a963bffe13d 100644
--- a/htdocs/langs/fr_FR/projects.lang
+++ b/htdocs/langs/fr_FR/projects.lang
@@ -268,3 +268,5 @@ OneLinePerTask=Une ligne par tâche
 OneLinePerPeriod=Une ligne par période
 RefTaskParent=Réf. Tâche parent
 ProfitIsCalculatedWith=Le bénéfice est calculé sur la base de
+PROJECT_CLASSIFY_CLOSED_WHEN_ALL_TASKS_DONE=Classer le projet à clôturé lorsque toutes les tâches de ce projet sont à 100 %% de progression
+PROJECT_CLASSIFY_CLOSED_WHEN_ALL_TASKS_DONE_help=Non rétroactif : l’activation de cette option ne clôturera pas les projets dont les tâches sont déjà à 100 %%. Cette option ne classe que les projets ouverts.
diff --git a/htdocs/projet/admin/project.php b/htdocs/projet/admin/project.php
index f36aae34c4f..45e62eafbe9 100644
--- a/htdocs/projet/admin/project.php
+++ b/htdocs/projet/admin/project.php
@@ -244,6 +244,12 @@ elseif ($action == 'setdoc')
 	}
 }
 
+// Set boolean (on/off) constants
+elseif (preg_match('/^(set|del)_?([A-Z_]+)$/', $action, $reg)) {
+	if (!dolibarr_set_const($db, $reg[2], ($reg[1] === 'set' ? '1' : '0'), 'chaine', 0, '', $conf->entity) > 0) {
+		dol_print_error($db);
+	}
+}
 
 /*
  * View
@@ -840,6 +846,16 @@ print $form->textwithpicto('', $langs->trans('AllowToLinkFromOtherCompany'));
 print '<input type="submit" class="button" name="PROJECT_ALLOW_TO_LINK_FROM_OTHER_COMPANY" value="'.$langs->trans("Modify").'">';
 print '</td>';
 
+$key = 'PROJECT_CLASSIFY_CLOSED_WHEN_ALL_TASKS_DONE';
+echo '<tr class="oddeven">',
+		'<td class="left">',
+			$form->textwithpicto($langs->transnoentities($key), $langs->transnoentities($key . '_help')),
+		'</td>',
+		'<td class="right" colspan="2">',
+			ajax_constantonoff($key),
+		'</td>',
+	'</tr>';
+
 print '</table>';
 
 
diff --git a/htdocs/projet/class/task.class.php b/htdocs/projet/class/task.class.php
index b4733de05ae..a2e670906ca 100644
--- a/htdocs/projet/class/task.class.php
+++ b/htdocs/projet/class/task.class.php
@@ -383,13 +383,35 @@ class Task extends CommonObject
 
 		// Update extrafield
 		if (!$error) {
-			if (!$error)
+			$result = $this->insertExtraFields();
+			if ($result < 0)
 			{
-				$result = $this->insertExtraFields();
-				if ($result < 0)
-				{
-					$error++;
+				$error++;
+			}
+		}
+
+		if (!$error && $conf->global->PROJECT_CLASSIFY_CLOSED_WHEN_ALL_TASKS_DONE) {
+			// Close the parent project if it is open (validated) and its tasks are 100% completed
+			$project = new Project($this->db);
+			if ($project->fetch($this->fk_project) > 0 && $project->statut == Project::STATUS_VALIDATED) {
+				$project->getLinesArray(null); // this method does not return <= 0 if fails
+				$projectCompleted = array_reduce(
+					$project->lines,
+					function ($allTasksCompleted, $task) {
+						return $allTasksCompleted && $task->progress >= 100;
+					},
+					1
+				);
+				if ($projectCompleted) {
+					if ($project->setClose($user) <= 0) {
+						$error++;
+					}
 				}
+			} else {
+				$error++;
+			}
+			if ($error) {
+				$this->errors[] = $project->error;
 			}
 		}