diff --git a/libs/ardour/export_graph_builder.cc b/libs/ardour/export_graph_builder.cc
index 6d7a36f5cc..1cd3118eae 100644
--- a/libs/ardour/export_graph_builder.cc
+++ b/libs/ardour/export_graph_builder.cc
@@ -40,11 +40,11 @@ ExportGraphBuilder::~ExportGraphBuilder ()
 int
 ExportGraphBuilder::process (nframes_t frames, bool last_cycle)
 {
-	assert(frames == process_buffer_frames);
+	assert(frames <= process_buffer_frames);
 	
 	for (ChannelMap::iterator it = channels.begin(); it != channels.end(); ++it) {
-		it->first->read (process_buffer, process_buffer_frames);
-		ProcessContext<Sample> context(process_buffer, process_buffer_frames, 1);
+		it->first->read (process_buffer, frames);
+		ProcessContext<Sample> context(process_buffer, frames, 1);
 		if (last_cycle) { context.set_flag (ProcessContext<Sample>::EndOfInput); }
 		it->second->process (context);
 	}