diff --git a/vvp/vpi_callback.cc b/vvp/vpi_callback.cc
index b9f9b1e60..3ee85f2f4 100644
--- a/vvp/vpi_callback.cc
+++ b/vvp/vpi_callback.cc
@@ -316,7 +316,9 @@ void sync_cb::run_run()
       if (cur->cb_data.cb_rtn != 0) {
 	    assert(vpi_mode_flag == VPI_MODE_NONE);
 	    vpi_mode_flag = sync_flag? VPI_MODE_ROSYNC : VPI_MODE_RWSYNC;
+	    vpip_cur_task = dynamic_cast<__vpiSysTaskCall*>(cur->cb_data.obj);
 	    (cur->cb_data.cb_rtn)(&cur->cb_data);
+	    vpip_cur_task = 0;
 	    vpi_mode_flag = VPI_MODE_NONE;
       }
 
diff --git a/vvp/vpi_tasks.cc b/vvp/vpi_tasks.cc
index 31368b391..b0aa19bfa 100644
--- a/vvp/vpi_tasks.cc
+++ b/vvp/vpi_tasks.cc
@@ -978,6 +978,7 @@ void vpip_execute_vpi_call(vthread_t thr, vpiHandle ref)
       else if (sysfunc_vec4*func_vec4 = dynamic_cast<sysfunc_vec4*>(ref)) {
 	    vthread_push_vec4(thr, func_vec4->return_value());
       }
+      vpip_cur_task = 0;
 }
 
 /*