diff --git a/io/task.c b/io/task.c
index 64c4c7126a..1ae7b86488 100644
--- a/io/task.c
+++ b/io/task.c
@@ -136,6 +136,7 @@ static gpointer qio_task_thread_worker(gpointer opaque)
                           qio_task_thread_result, task, NULL);
     g_source_attach(task->thread->completion,
                     task->thread->context);
+    g_source_unref(task->thread->completion);
     trace_qio_task_thread_source_attach(task, task->thread->completion);
 
     qemu_cond_signal(&task->thread_cond);