diff -u -r dbus-1.8.20/dbus/dbus-connection.c dbus-1.8.20-patch/dbus/dbus-connection.c
--- dbus-1.8.20/dbus/dbus-connection.c	2015-05-14 13:23:25.000000000 +0100
+++ dbus-1.8.20-patch/dbus/dbus-connection.c	2017-09-18 11:27:57.510653542 +0100
@@ -325,6 +325,7 @@
   unsigned int disconnected_message_processed : 1; /**< We did our default handling of the disconnected message,
                                                     * such as closing the connection.
                                                     */
+  unsigned int processing : 1; /**< TRUE if dispatch processing is in progress */
   
 #ifndef DBUS_DISABLE_CHECKS
   unsigned int have_connection_lock : 1; /**< Used to check locking */
@@ -1222,6 +1223,14 @@
         {
           _dbus_verbose ("pending call completed while acquiring I/O path (reply found in queue)");
         }
+      else if ( (pending != NULL) && (_dbus_pending_call_get_processing_unlocked(pending)) )
+        {
+          _dbus_verbose ("pending call processing while acquiring I/O path");
+        }
+      else if ( connection->processing )
+        {
+          _dbus_verbose ("connection processing while acquiring I/O path");
+        }
       else
         {
           _dbus_transport_do_iteration (connection->transport,
@@ -2525,7 +2534,7 @@
         {          
           /* block again, we don't have the reply buffered yet. */
           _dbus_connection_do_iteration_unlocked (connection,
-                                                  NULL,
+                                                  pending,
                                                   DBUS_ITERATION_DO_READING |
                                                   DBUS_ITERATION_BLOCK,
                                                   timeout_milliseconds - elapsed_milliseconds);
@@ -4622,11 +4631,14 @@
                                          reply_serial);
   if (pending)
     {
+      connection->processing = 1;
+      _dbus_pending_call_processing(pending);
       _dbus_verbose ("Dispatching a pending reply\n");
       complete_pending_call_and_unlock (connection, pending, message);
       pending = NULL; /* it's probably unref'd */
       
       CONNECTION_LOCK (connection);
+      connection->processing = 0;
       _dbus_verbose ("pending call completed in dispatch\n");
       result = DBUS_HANDLER_RESULT_HANDLED;
       goto out;
diff -u -r dbus-1.8.20/dbus/dbus-pending-call.c dbus-1.8.20-patch/dbus/dbus-pending-call.c
--- dbus-1.8.20/dbus/dbus-pending-call.c	2015-05-14 13:23:04.000000000 +0100
+++ dbus-1.8.20-patch/dbus/dbus-pending-call.c	2017-09-18 13:01:36.453913127 +0100
@@ -77,6 +77,7 @@
 
   unsigned int completed : 1;                     /**< TRUE if completed */
   unsigned int timeout_added : 1;                 /**< Have added the timeout */
+  unsigned int processing : 1;                    /**< Processing has started */
 };
 
 static void
@@ -194,6 +195,20 @@
 }
 
 /**
+ * Marks the call as having started processing.
+ *
+ * @param pending the pending call
+ *
+ */
+void
+_dbus_pending_call_processing (DBusPendingCall *pending)
+{
+  _dbus_assert (!pending->processing);
+
+  pending->processing = TRUE;
+}
+
+/**
  * Calls notifier function for the pending call
  * and sets the call to completed.
  *
@@ -482,6 +497,19 @@
   return pending->completed;
 }
 
+/**
+ * Checks whether the pending call has started processing
+ * yet, or not. Assumes connection lock is held.
+ *
+ * @param pending the pending call
+ * @returns #TRUE if the pending call has started processing
+ */
+dbus_bool_t
+_dbus_pending_call_get_processing_unlocked (DBusPendingCall    *pending)
+{
+  return pending->processing;
+}
+
 static DBusDataSlotAllocator slot_allocator =
   _DBUS_DATA_SLOT_ALLOCATOR_INIT (_DBUS_LOCK_NAME (pending_call_slots));
 
diff -u -r dbus-1.8.20/dbus/dbus-pending-call-internal.h dbus-1.8.20-patch/dbus/dbus-pending-call-internal.h
--- dbus-1.8.20/dbus/dbus-pending-call-internal.h	2015-05-14 13:23:25.000000000 +0100
+++ dbus-1.8.20-patch/dbus/dbus-pending-call-internal.h	2017-09-18 10:26:10.230037445 +0100
@@ -41,7 +41,9 @@
 DBusConnection * _dbus_pending_call_get_connection_and_lock      (DBusPendingCall    *pending);
 DBusConnection * _dbus_pending_call_get_connection_unlocked      (DBusPendingCall    *pending);
 dbus_bool_t      _dbus_pending_call_get_completed_unlocked       (DBusPendingCall    *pending);
+dbus_bool_t      _dbus_pending_call_get_processing_unlocked      (DBusPendingCall    *pending);
 void             _dbus_pending_call_complete                     (DBusPendingCall    *pending);
+void             _dbus_pending_call_processing                   (DBusPendingCall    *pending);
 void             _dbus_pending_call_set_reply_unlocked           (DBusPendingCall    *pending,
                                                                   DBusMessage        *message);
 void             _dbus_pending_call_queue_timeout_error_unlocked (DBusPendingCall    *pending,