diff --git a/include/maxscale/worker.hh b/include/maxscale/worker.hh
index de5801607..d6fc21bcb 100644
--- a/include/maxscale/worker.hh
+++ b/include/maxscale/worker.hh
@@ -672,10 +672,11 @@ public:
      * The worker will run the poll loop, until it is told to shut down.
      *
      * @attention  This function will run in the calling thread.
-     *
-     * @param pSem Semaphore that is posted on once the thread has started
      */
-    void run(mxb::Semaphore* pSem = NULL);
+    void run()
+    {
+        run(nullptr);
+    }
 
     /**
      * Run worker in separate thread.
@@ -1195,6 +1196,8 @@ private:
         }
     };
 
+    void run(mxb::Semaphore* pSem);
+
     typedef DelegatingTimer<Worker>                         PrivateTimer;
     typedef std::multimap<int64_t, DelayedCall*>            DelayedCallsByTime;
     typedef std::unordered_map<uint32_t, DelayedCall*>      DelayedCallsById;
diff --git a/server/core/worker.cc b/server/core/worker.cc
index 3fb008040..ef18299c2 100644
--- a/server/core/worker.cc
+++ b/server/core/worker.cc
@@ -529,6 +529,7 @@ bool Worker::post_message(uint32_t msg_id, intptr_t arg1, intptr_t arg2)
 
 void Worker::run(mxb::Semaphore* pSem)
 {
+    ss_dassert(m_state == STOPPED);
     this_thread.pCurrent_worker = this;
 
     if (pre_run())