diff --git a/mistral/engine/task_handler.py b/mistral/engine/task_handler.py
index bf58c1c4f..b180f2088 100644
--- a/mistral/engine/task_handler.py
+++ b/mistral/engine/task_handler.py
@@ -409,32 +409,43 @@ def _refresh_task_state(task_ex_id):
 
         wf_ctrl = wf_base.get_controller(wf_ex, wf_spec)
 
-        log_state = wf_ctrl.get_logical_task_state(task_ex)
+        with db_api.named_lock(task_ex.id):
+            # NOTE: we have to use this lock to prevent two (or more) such
+            # methods from changing task state and starting its action or
+            # workflow. Checking task state outside of this section is a
+            # performance optimization because locking is pretty expensive.
+            db_api.refresh(task_ex)
 
-        state = log_state.state
-        state_info = log_state.state_info
+            if (states.is_completed(task_ex.state)
+                    or task_ex.state == states.RUNNING):
+                return
 
-        # Update 'triggered_by' because it could have changed.
-        task_ex.runtime_context['triggered_by'] = log_state.triggered_by
+            log_state = wf_ctrl.get_logical_task_state(task_ex)
 
-        if state == states.RUNNING:
-            continue_task(task_ex)
-        elif state == states.ERROR:
-            complete_task(task_ex, state, state_info)
-        elif state == states.WAITING:
-            LOG.info(
-                "Task execution is still in WAITING state"
-                " [task_ex_id=%s, task_name=%s]",
-                task_ex_id,
-                task_ex.name
-            )
-        else:
-            # Must never get here.
-            raise RuntimeError(
-                'Unexpected logical task state [task_ex_id=%s, '
-                'task_name=%s, state=%s]' %
-                (task_ex_id, task_ex.name, state)
-            )
+            state = log_state.state
+            state_info = log_state.state_info
+
+            # Update 'triggered_by' because it could have changed.
+            task_ex.runtime_context['triggered_by'] = log_state.triggered_by
+
+            if state == states.RUNNING:
+                continue_task(task_ex)
+            elif state == states.ERROR:
+                complete_task(task_ex, state, state_info)
+            elif state == states.WAITING:
+                LOG.info(
+                    "Task execution is still in WAITING state"
+                    " [task_ex_id=%s, task_name=%s]",
+                    task_ex_id,
+                    task_ex.name
+                )
+            else:
+                # Must never get here.
+                raise RuntimeError(
+                    'Unexpected logical task state [task_ex_id=%s, '
+                    'task_name=%s, state=%s]' %
+                    (task_ex_id, task_ex.name, state)
+                )
 
 
 def _schedule_refresh_task_state(task_ex_id, delay=0):