diff --git a/python/core/auto_generated/qgstaskmanager.sip.in b/python/core/auto_generated/qgstaskmanager.sip.in
index 737e0fdbee7..fa1d4067903 100644
--- a/python/core/auto_generated/qgstaskmanager.sip.in
+++ b/python/core/auto_generated/qgstaskmanager.sip.in
@@ -331,7 +331,7 @@ the task. The priority argument can be used to control the run queue's
 order of execution, with larger numbers
 taking precedence over lower priority numbers.
 
-:return: unique task ID
+:return: unique task ID, or 0 if task could not be added
 %End
 
     long addTask( const TaskDefinition &task /Transfer/, int priority = 0 );
@@ -342,7 +342,7 @@ manager will be responsible for starting the task. The priority argument can
 be used to control the run queue's order of execution, with larger numbers
 taking precedence over lower priority numbers.
 
-:return: unique task ID
+:return: unique task ID, or 0 if task could not be added
 %End
 
     QgsTask *task( long id ) const;
diff --git a/src/core/qgstaskmanager.cpp b/src/core/qgstaskmanager.cpp
index 5ab17b75baa..fa1256125d2 100644
--- a/src/core/qgstaskmanager.cpp
+++ b/src/core/qgstaskmanager.cpp
@@ -390,6 +390,9 @@ long QgsTaskManager::addTask( const QgsTaskManager::TaskDefinition &definition,
 
 long QgsTaskManager::addTaskPrivate( QgsTask *task, QgsTaskList dependencies, bool isSubTask, int priority )
 {
+  if ( !task )
+    return 0;
+
   long taskId = mNextTaskId++;
 
   mTaskMutex->lock();
diff --git a/src/core/qgstaskmanager.h b/src/core/qgstaskmanager.h
index 8796cc2f40e..70df3a389d4 100644
--- a/src/core/qgstaskmanager.h
+++ b/src/core/qgstaskmanager.h
@@ -405,7 +405,7 @@ class CORE_EXPORT QgsTaskManager : public QObject
      * the task. The priority argument can be used to control the run queue's
      * order of execution, with larger numbers
      * taking precedence over lower priority numbers.
-     * \returns unique task ID
+     * \returns unique task ID, or 0 if task could not be added
      */
     long addTask( QgsTask *task SIP_TRANSFER, int priority = 0 );
 
@@ -415,7 +415,7 @@ class CORE_EXPORT QgsTaskManager : public QObject
      * manager will be responsible for starting the task. The priority argument can
      * be used to control the run queue's order of execution, with larger numbers
      * taking precedence over lower priority numbers.
-     * \returns unique task ID
+     * \returns unique task ID, or 0 if task could not be added
      */
     long addTask( const TaskDefinition &task SIP_TRANSFER, int priority = 0 );
 
@@ -573,7 +573,7 @@ class CORE_EXPORT QgsTaskManager : public QObject
     QMap< long, QgsWeakMapLayerPointerList > mLayerDependencies;
 
     //! Tracks the next unique task ID
-    long mNextTaskId = 0;
+    long mNextTaskId = 1;
 
     //! List of active (queued or running) tasks. Includes subtasks.
     QSet< QgsTask * > mActiveTasks;
diff --git a/tests/src/core/testqgstaskmanager.cpp b/tests/src/core/testqgstaskmanager.cpp
index d9b987c23b2..917af97492d 100644
--- a/tests/src/core/testqgstaskmanager.cpp
+++ b/tests/src/core/testqgstaskmanager.cpp
@@ -329,14 +329,17 @@ void TestQgsTaskManager::addTask()
 
   QSignalSpy spy( &manager, &QgsTaskManager::taskAdded );
 
+  // null task
+  QVERIFY( !manager.addTask( nullptr ) );
+
   //add a task
   CancelableTask *task = new CancelableTask();
   long id = manager.addTask( task );
-  QCOMPARE( id, 0L );
+  QCOMPARE( id, 1L );
   QCOMPARE( manager.tasks().count(), 1 );
   QCOMPARE( manager.count(), 1 );
   QCOMPARE( spy.count(), 1 );
-  QCOMPARE( spy.last().at( 0 ).toLongLong(), 0LL );
+  QCOMPARE( spy.last().at( 0 ).toLongLong(), 1LL );
   while ( !task->isActive() )
   {
     QCoreApplication::processEvents();
@@ -346,18 +349,18 @@ void TestQgsTaskManager::addTask()
   QCOMPARE( task->status(), QgsTask::Running );
 
   //retrieve task
-  QCOMPARE( manager.task( 0L ), task );
+  QCOMPARE( manager.task( 1L ), task );
   QCOMPARE( manager.tasks().at( 0 ), task );
 
   //add a second task
   CancelableTask *task2 = new CancelableTask();
   id = manager.addTask( task2 );
-  QCOMPARE( id, 1L );
+  QCOMPARE( id, 2L );
   QCOMPARE( manager.tasks().count(), 2 );
   QCOMPARE( manager.count(), 2 );
-  QCOMPARE( manager.task( 0L ), task );
+  QCOMPARE( manager.task( 1L ), task );
   QVERIFY( manager.tasks().contains( task ) );
-  QCOMPARE( manager.task( 1L ), task2 );
+  QCOMPARE( manager.task( 2L ), task2 );
   QVERIFY( manager.tasks().contains( task2 ) );
   while ( !task2->isActive() )
   {
@@ -368,7 +371,7 @@ void TestQgsTaskManager::addTask()
   QCOMPARE( task2->status(), QgsTask::Running );
 
   QCOMPARE( spy.count(), 2 );
-  QCOMPARE( spy.last().at( 0 ).toLongLong(), 1LL );
+  QCOMPARE( spy.last().at( 0 ).toLongLong(), 2LL );
 
   task->cancel();
   task2->cancel();
@@ -649,8 +652,8 @@ void TestQgsTaskManager::taskId()
   TestTask *task3 = new TestTask();
 
   QCOMPARE( manager.taskId( nullptr ), -1L );
-  QCOMPARE( manager.taskId( task ), 0L );
-  QCOMPARE( manager.taskId( task2 ), 1L );
+  QCOMPARE( manager.taskId( task ), 1L );
+  QCOMPARE( manager.taskId( task2 ), 2L );
   QCOMPARE( manager.taskId( task3 ), -1L );
 
   delete task3;
@@ -725,7 +728,7 @@ void TestQgsTaskManager::progressChanged()
 
   QCOMPARE( task->progress(), 50.0 );
   QCOMPARE( spy.count(), 1 );
-  QCOMPARE( spy.last().at( 0 ).toLongLong(), 0LL );
+  QCOMPARE( spy.last().at( 0 ).toLongLong(), 1LL );
   QCOMPARE( spy.last().at( 1 ).toDouble(), 50.0 );
   //multiple running tasks, so finalTaskProgressChanged(double) should not be emitted
   QCOMPARE( spy2.count(), 0 );
@@ -733,7 +736,7 @@ void TestQgsTaskManager::progressChanged()
   task2->emitProgressChanged( 75.0 );
   QCOMPARE( task2->progress(), 75.0 );
   QCOMPARE( spy.count(), 2 );
-  QCOMPARE( spy.last().at( 0 ).toLongLong(), 1LL );
+  QCOMPARE( spy.last().at( 0 ).toLongLong(), 2LL );
   QCOMPARE( spy.last().at( 1 ).toDouble(), 75.0 );
   QCOMPARE( spy2.count(), 0 );
 
@@ -799,7 +802,7 @@ void TestQgsTaskManager::statusChanged()
   flushEvents();
 
   QCOMPARE( spy.count(), 1 );
-  QCOMPARE( spy.last().at( 0 ).toLongLong(), 1LL );
+  QCOMPARE( spy.last().at( 0 ).toLongLong(), 2LL );
   QCOMPARE( static_cast< QgsTask::TaskStatus >( spy.last().at( 1 ).toInt() ), QgsTask::Running );
 
   task->terminate();
@@ -809,7 +812,7 @@ void TestQgsTaskManager::statusChanged()
   }
   flushEvents();
   QCOMPARE( spy.count(), 2 );
-  QCOMPARE( spy.last().at( 0 ).toLongLong(), 0LL );
+  QCOMPARE( spy.last().at( 0 ).toLongLong(), 1LL );
   QCOMPARE( static_cast< QgsTask::TaskStatus >( spy.last().at( 1 ).toInt() ), QgsTask::Terminated );
 
   task2->finish();
@@ -819,7 +822,7 @@ void TestQgsTaskManager::statusChanged()
   }
   flushEvents();
   QCOMPARE( spy.count(), 3 );
-  QCOMPARE( spy.last().at( 0 ).toLongLong(), 1LL );
+  QCOMPARE( spy.last().at( 0 ).toLongLong(), 2LL );
   QCOMPARE( static_cast< QgsTask::TaskStatus >( spy.last().at( 1 ).toInt() ), QgsTask::Complete );
 }
 
@@ -1126,7 +1129,7 @@ void TestQgsTaskManager::managerWithSubTasks()
   QCOMPARE( spyProgress.count(), 0 );
   subTask->emitProgressChanged( 50 );
   QCOMPARE( spyProgress.count(), 1 );
-  QCOMPARE( spyProgress.last().at( 0 ).toLongLong(), 0LL );
+  QCOMPARE( spyProgress.last().at( 0 ).toLongLong(), 1LL );
   // subTask itself is 50% done, so with it's child task it's sitting at overall 25% done
   // (one task 50%, one task not started)
   // parent task has two tasks (itself + subTask), and subTask is 25% done.... so parent
@@ -1135,11 +1138,11 @@ void TestQgsTaskManager::managerWithSubTasks()
 
   subsubTask->emitProgressChanged( 100 );
   QCOMPARE( spyProgress.count(), 2 );
-  QCOMPARE( spyProgress.last().at( 0 ).toLongLong(), 0LL );
+  QCOMPARE( spyProgress.last().at( 0 ).toLongLong(), 1LL );
   QCOMPARE( spyProgress.last().at( 1 ).toInt(), 38 );
   parent->emitProgressChanged( 50 );
   QCOMPARE( spyProgress.count(), 3 );
-  QCOMPARE( spyProgress.last().at( 0 ).toLongLong(), 0LL );
+  QCOMPARE( spyProgress.last().at( 0 ).toLongLong(), 1LL );
   QCOMPARE( spyProgress.last().at( 1 ).toInt(), 63 );
 
   //manager should not emit statusChanged signals for subtasks
@@ -1152,7 +1155,7 @@ void TestQgsTaskManager::managerWithSubTasks()
   }
   flushEvents();
   QCOMPARE( statusSpy.count(), 1 );
-  QCOMPARE( statusSpy.last().at( 0 ).toLongLong(), 0LL );
+  QCOMPARE( statusSpy.last().at( 0 ).toLongLong(), 1LL );
   QCOMPARE( static_cast< QgsTask::TaskStatus >( statusSpy.last().at( 1 ).toInt() ), QgsTask::Running );
 
   subTask->finish();
@@ -1170,7 +1173,7 @@ void TestQgsTaskManager::managerWithSubTasks()
   }
   flushEvents();
   QCOMPARE( statusSpy.count(), 2 );
-  QCOMPARE( statusSpy.last().at( 0 ).toLongLong(), 0LL );
+  QCOMPARE( statusSpy.last().at( 0 ).toLongLong(), 1LL );
   QCOMPARE( static_cast< QgsTask::TaskStatus >( statusSpy.last().at( 1 ).toInt() ), QgsTask::Complete );