diff --git a/tpool/aio_linux.cc b/tpool/aio_linux.cc
index 6997cbcccab..1f52e62bd07 100644
--- a/tpool/aio_linux.cc
+++ b/tpool/aio_linux.cc
@@ -102,6 +102,7 @@ class aio_linux final : public aio
     */
     constexpr unsigned MAX_EVENTS= 256;
 
+    aio->m_pool->m_worker_init_callback();
     io_event events[MAX_EVENTS];
     for (;;)
     {
@@ -110,14 +111,14 @@ class aio_linux final : public aio
         continue;
       case -EINVAL:
         if (shutdown_in_progress)
-          return;
+          goto end;
         /* fall through */
       default:
         if (ret < 0)
         {
           fprintf(stderr, "io_getevents returned %d\n", ret);
           abort();
-          return;
+          goto end;
         }
         for (int i= 0; i < ret; i++)
         {
@@ -142,6 +143,8 @@ class aio_linux final : public aio
         }
       }
     }
+end:
+    aio->m_pool->m_worker_destroy_callback();
   }
 
 public:
diff --git a/tpool/aio_win.cc b/tpool/aio_win.cc
index eec37383152..f483e3ca1e1 100644
--- a/tpool/aio_win.cc
+++ b/tpool/aio_win.cc
@@ -92,7 +92,9 @@ public:
 
   static void aio_completion_thread_proc(tpool_generic_win_aio* aio)
   {
+    aio->m_pool->m_worker_init_callback();
     aio->completion_thread_work();
+    aio->m_pool->m_worker_destroy_callback();
   }
 
   ~tpool_generic_win_aio()
diff --git a/tpool/tpool.h b/tpool/tpool.h
index 7ac6763ae23..a5dccca5e91 100644
--- a/tpool/tpool.h
+++ b/tpool/tpool.h
@@ -27,6 +27,8 @@ Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02111 - 1301 USA*/
 #define NOMINMAX
 #endif
 #include <windows.h>
+#include <cassert>
+
 /**
   Windows-specific native file handle struct.
   Apart from the actual handle, contains PTP_IO
@@ -202,21 +204,24 @@ protected:
   std::unique_ptr<aio> m_aio;
   virtual aio *create_native_aio(int max_io)= 0;
 
+public:
   /**
     Functions to be called at worker thread start/end
     can be used for example to set some TLS variables
   */
-  void (*m_worker_init_callback)(void);
-  void (*m_worker_destroy_callback)(void);
+  void (*m_worker_init_callback)(void)= [] {};
+  void (*m_worker_destroy_callback)(void)= [] {};
 
-public:
-  thread_pool() : m_aio(), m_worker_init_callback(), m_worker_destroy_callback()
+  thread_pool()
+      : m_aio()
   {
   }
   virtual void submit_task(task *t)= 0;
   virtual timer* create_timer(callback_func func, void *data=nullptr) = 0;
   void set_thread_callbacks(void (*init)(), void (*destroy)())
   {
+    assert(init);
+    assert(destroy);
     m_worker_init_callback= init;
     m_worker_destroy_callback= destroy;
   }
diff --git a/tpool/tpool_generic.cc b/tpool/tpool_generic.cc
index 9697194e0b2..cd4dd5f0bde 100644
--- a/tpool/tpool_generic.cc
+++ b/tpool/tpool_generic.cc
@@ -571,8 +571,7 @@ void thread_pool_generic::worker_main(worker_data *thread_var)
 {
   task* task;
   set_tls_pool(this);
-  if(m_worker_init_callback)
-   m_worker_init_callback();
+  m_worker_init_callback();
 
   tls_worker_data = thread_var;
 
@@ -581,8 +580,7 @@ void thread_pool_generic::worker_main(worker_data *thread_var)
     task->execute();
   }
 
-  if (m_worker_destroy_callback)
-    m_worker_destroy_callback();
+  m_worker_destroy_callback();
 
   worker_end(thread_var);
 }
diff --git a/tpool/tpool_win.cc b/tpool/tpool_win.cc
index 2b413b8d1b6..c012c4b6408 100644
--- a/tpool/tpool_win.cc
+++ b/tpool/tpool_win.cc
@@ -45,9 +45,7 @@ class thread_pool_win : public thread_pool
       if (!m_pool)
         return;
 
-      if (m_pool->m_worker_destroy_callback)
-        m_pool->m_worker_destroy_callback();
-
+      m_pool->m_worker_destroy_callback();
       m_pool->m_thread_count--;
     }
     /** This needs to be called before every IO or simple task callback.*/
@@ -63,8 +61,7 @@ class thread_pool_win : public thread_pool
       m_pool = pool;
       m_pool->m_thread_count++;
       // Call the thread init function.
-      if (m_pool->m_worker_init_callback)
-        m_pool->m_worker_init_callback();
+      m_pool->m_worker_init_callback();
     }
   };