diff --git a/wagtail/admin/tests/test_workflows.py b/wagtail/admin/tests/test_workflows.py
index 33b7e13768..b3413db9bb 100644
--- a/wagtail/admin/tests/test_workflows.py
+++ b/wagtail/admin/tests/test_workflows.py
@@ -923,6 +923,8 @@ class TestDisableViews(TestCase, WagtailTestUtils):
         self.assertEqual(states.filter(status=WorkflowState.STATUS_IN_PROGRESS).count(), 0)
         self.assertEqual(states.filter(status=WorkflowState.STATUS_CANCELLED).count(), 1)
 
+        self.assertEqual(TaskState.objects.filter(workflow_state__workflow=self.workflow, status=TaskState.STATUS_IN_PROGRESS).count(), 0)
+
     def test_disable_task(self):
         """Test that deactivating a task sets it to inactive and cancels in progress states"""
         self.login(self.submitter)
diff --git a/wagtail/core/models.py b/wagtail/core/models.py
index f74cb6e915..a1b8438d60 100644
--- a/wagtail/core/models.py
+++ b/wagtail/core/models.py
@@ -2837,6 +2837,9 @@ class WorkflowState(models.Model):
     def update(self, user=None, next_task=None):
         """Checks the status of the current task, and progresses (or ends) the workflow if appropriate. If the workflow progresses,
         next_task will be used to start a specific task next if provided."""
+        if self.status != self.STATUS_IN_PROGRESS:
+            # Updating a completed or cancelled workflow should have no effect
+            return
         try:
             current_status = self.current_task_state.status
         except AttributeError:
@@ -2880,6 +2883,9 @@ class WorkflowState(models.Model):
             raise PermissionDenied
         self.status = self.STATUS_CANCELLED
         self.save()
+        for state in self.task_states.filter(status=TaskState.STATUS_IN_PROGRESS):
+            # Cancel all in progress task states
+            state.specific.cancel(user=user)
         workflow_cancelled.send(sender=self.__class__, instance=self, user=user)
 
     @transaction.atomic