diff --git a/gio/gdbusprivate.c b/gio/gdbusprivate.c
index e8121339e..da9388a2a 100644
--- a/gio/gdbusprivate.c
+++ b/gio/gdbusprivate.c
@@ -334,6 +334,13 @@ _g_dbus_shared_thread_unref (SharedThreadData *data)
 
 /* ---------------------------------------------------------------------------------------------------- */
 
+typedef enum {
+    PENDING_NONE = 0,
+    PENDING_WRITE,
+    PENDING_FLUSH,
+    PENDING_CLOSE
+} OutputPending;
+
 struct GDBusWorker
 {
   volatile gint                       ref_count;
@@ -371,12 +378,12 @@ struct GDBusWorker
   GSocketControlMessage             **read_ancillary_messages;
   gint                                read_num_ancillary_messages;
 
-  /* TRUE if an async write, flush or close is pending.
+  /* Whether an async write, flush or close, or none of those, is pending.
    * Only the worker thread may change its value, and only with the write_lock.
    * Other threads may read its value when holding the write_lock.
    * The worker thread may read its value at any time.
    */
-  gboolean                            output_pending;
+  OutputPending                       output_pending;
   /* used for writing */
   GMutex                             *write_lock;
   /* queue of MessageToWriteData, protected by write_lock */
@@ -906,7 +913,7 @@ static void write_message_continue_writing (MessageToWriteData *data);
 /* called in private thread shared by all GDBusConnection instances
  *
  * write-lock is not held on entry
- * output_pending is true on entry
+ * output_pending is PENDING_WRITE on entry
  */
 static void
 write_message_async_cb (GObject      *source_object,
@@ -956,7 +963,7 @@ write_message_async_cb (GObject      *source_object,
 /* called in private thread shared by all GDBusConnection instances
  *
  * write-lock is not held on entry
- * output_pending is true on entry
+ * output_pending is PENDING_WRITE on entry
  */
 static gboolean
 on_socket_ready (GSocket      *socket,
@@ -971,7 +978,7 @@ on_socket_ready (GSocket      *socket,
 /* called in private thread shared by all GDBusConnection instances
  *
  * write-lock is not held on entry
- * output_pending is true on entry
+ * output_pending is PENDING_WRITE on entry
  */
 static void
 write_message_continue_writing (MessageToWriteData *data)
@@ -1108,7 +1115,7 @@ write_message_continue_writing (MessageToWriteData *data)
 /* called in private thread shared by all GDBusConnection instances
  *
  * write-lock is not held on entry
- * output_pending is true on entry
+ * output_pending is PENDING_WRITE on entry
  */
 static void
 write_message_async (GDBusWorker         *worker,
@@ -1166,7 +1173,7 @@ flush_data_list_complete (const GList  *flushers,
 /* called in private thread shared by all GDBusConnection instances
  *
  * write-lock is not held on entry
- * output_pending is true on entry
+ * output_pending is PENDING_FLUSH on entry
  */
 static void
 ostream_flush_cb (GObject      *source_object,
@@ -1204,8 +1211,8 @@ ostream_flush_cb (GObject      *source_object,
   /* Make sure we tell folks that we don't have additional
      flushes pending */
   g_mutex_lock (data->worker->write_lock);
-  g_assert (data->worker->output_pending);
-  data->worker->output_pending = FALSE;
+  g_assert (data->worker->output_pending == PENDING_FLUSH);
+  data->worker->output_pending = PENDING_NONE;
   g_mutex_unlock (data->worker->write_lock);
 
   /* OK, cool, finally kick off the next write */
@@ -1218,7 +1225,7 @@ ostream_flush_cb (GObject      *source_object,
 /* called in private thread shared by all GDBusConnection instances
  *
  * write-lock is not held on entry
- * output_pending is false on entry
+ * output_pending is PENDING_NONE on entry
  */
 static void
 message_written (GDBusWorker *worker,
@@ -1266,8 +1273,8 @@ message_written (GDBusWorker *worker,
     }
   if (flushers != NULL)
     {
-      g_assert (!worker->output_pending);
-      worker->output_pending = TRUE;
+      g_assert (worker->output_pending == PENDING_NONE);
+      worker->output_pending = PENDING_FLUSH;
     }
   g_mutex_unlock (worker->write_lock);
 
@@ -1294,7 +1301,7 @@ message_written (GDBusWorker *worker,
 /* called in private thread shared by all GDBusConnection instances
  *
  * write-lock is not held on entry
- * output_pending is true on entry
+ * output_pending is PENDING_WRITE on entry
  */
 static void
 write_message_cb (GObject       *source_object,
@@ -1305,8 +1312,8 @@ write_message_cb (GObject       *source_object,
   GError *error;
 
   g_mutex_lock (data->worker->write_lock);
-  g_assert (data->worker->output_pending);
-  data->worker->output_pending = FALSE;
+  g_assert (data->worker->output_pending == PENDING_WRITE);
+  data->worker->output_pending = PENDING_NONE;
   g_mutex_unlock (data->worker->write_lock);
 
   error = NULL;
@@ -1329,7 +1336,7 @@ write_message_cb (GObject       *source_object,
 /* called in private thread shared by all GDBusConnection instances
  *
  * write-lock is not held on entry
- * output_pending is true on entry
+ * output_pending is PENDING_CLOSE on entry
  */
 static void
 iostream_close_cb (GObject      *source_object,
@@ -1354,8 +1361,8 @@ iostream_close_cb (GObject      *source_object,
   send_queue = worker->write_queue;
   worker->write_queue = g_queue_new ();
 
-  g_assert (worker->output_pending);
-  worker->output_pending = FALSE;
+  g_assert (worker->output_pending == PENDING_CLOSE);
+  worker->output_pending = PENDING_NONE;
 
   g_mutex_unlock (worker->write_lock);
 
@@ -1399,7 +1406,7 @@ iostream_close_cb (GObject      *source_object,
 /* called in private thread shared by all GDBusConnection instances
  *
  * write-lock is not held on entry
- * output_pending must be false on entry
+ * output_pending must be PENDING_NONE on entry
  */
 static void
 maybe_write_next_message (GDBusWorker *worker)
@@ -1408,7 +1415,7 @@ maybe_write_next_message (GDBusWorker *worker)
 
  write_next:
   /* we mustn't try to write two things at once */
-  g_assert (!worker->output_pending);
+  g_assert (worker->output_pending == PENDING_NONE);
 
   g_mutex_lock (worker->write_lock);
 
@@ -1416,7 +1423,7 @@ maybe_write_next_message (GDBusWorker *worker)
   if (worker->pending_close_attempts != NULL)
     {
       worker->close_expected = TRUE;
-      worker->output_pending = TRUE;
+      worker->output_pending = PENDING_CLOSE;
 
       g_io_stream_close_async (worker->stream, G_PRIORITY_DEFAULT,
                                NULL, iostream_close_cb,
@@ -1428,7 +1435,7 @@ maybe_write_next_message (GDBusWorker *worker)
       data = g_queue_pop_head (worker->write_queue);
 
       if (data != NULL)
-        worker->output_pending = TRUE;
+        worker->output_pending = PENDING_WRITE;
     }
 
   g_mutex_unlock (worker->write_lock);
@@ -1458,7 +1465,7 @@ maybe_write_next_message (GDBusWorker *worker)
         {
           /* filters dropped message */
           g_mutex_lock (worker->write_lock);
-          worker->output_pending = FALSE;
+          worker->output_pending = PENDING_NONE;
           g_mutex_unlock (worker->write_lock);
           message_to_write_data_free (data);
           goto write_next;
@@ -1499,7 +1506,7 @@ maybe_write_next_message (GDBusWorker *worker)
 /* called in private thread shared by all GDBusConnection instances
  *
  * write-lock is not held on entry
- * output_pending may be true or false
+ * output_pending may be anything
  */
 static gboolean
 write_message_in_idle_cb (gpointer user_data)
@@ -1509,7 +1516,7 @@ write_message_in_idle_cb (gpointer user_data)
   /* Because this is the worker thread, we can read this struct member
    * without holding the lock: no other thread ever modifies it.
    */
-  if (!worker->output_pending)
+  if (worker->output_pending == PENDING_NONE)
     maybe_write_next_message (worker);
 
   return FALSE;
@@ -1522,7 +1529,7 @@ write_message_in_idle_cb (gpointer user_data)
  * Can be called from any thread
  *
  * write_lock is not held on entry
- * output_pending may be true or false
+ * output_pending may be anything
  */
 static void
 schedule_write_in_worker_thread (GDBusWorker        *worker,
@@ -1538,7 +1545,7 @@ schedule_write_in_worker_thread (GDBusWorker        *worker,
     worker->pending_close_attempts = g_list_prepend (worker->pending_close_attempts,
                                                      close_data);
 
-  if (!worker->output_pending)
+  if (worker->output_pending == PENDING_NONE)
     {
       GSource *idle_source;
       idle_source = g_idle_source_new ();
@@ -1559,7 +1566,7 @@ schedule_write_in_worker_thread (GDBusWorker        *worker,
 /* can be called from any thread - steals blob
  *
  * write_lock is not held on entry
- * output_pending may be true or false
+ * output_pending may be anything
  */
 void
 _g_dbus_worker_send_message (GDBusWorker    *worker,
@@ -1612,7 +1619,7 @@ _g_dbus_worker_new (GIOStream                              *stream,
   worker->stream = g_object_ref (stream);
   worker->capabilities = capabilities;
   worker->cancellable = g_cancellable_new ();
-  worker->output_pending = FALSE;
+  worker->output_pending = PENDING_NONE;
 
   worker->frozen = initially_frozen;
   worker->received_messages_while_frozen = g_queue_new ();
@@ -1643,7 +1650,7 @@ _g_dbus_worker_new (GIOStream                              *stream,
 /* can be called from any thread
  *
  * write_lock is not held on entry
- * output_pending may be true or false
+ * output_pending may be anything
  */
 void
 _g_dbus_worker_close (GDBusWorker         *worker,
@@ -1670,7 +1677,7 @@ _g_dbus_worker_close (GDBusWorker         *worker,
  * worker - use your own synchronization primitive in the callbacks.
  *
  * write_lock is not held on entry
- * output_pending may be true or false
+ * output_pending may be anything
  */
 void
 _g_dbus_worker_stop (GDBusWorker *worker)
@@ -1696,7 +1703,7 @@ _g_dbus_worker_stop (GDBusWorker *worker)
  * the transport has been flushed
  *
  * write_lock is not held on entry
- * output_pending may be true or false
+ * output_pending may be anything
  */
 gboolean
 _g_dbus_worker_flush_sync (GDBusWorker    *worker,